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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS2020

Precise mass and radius of a transiting super-Earth planet orbiting the M dwarf TOI-1235: a planet in the radius gap?

We report the confirmation of a transiting planet around the bright weakly active M0.5 V star TOI-1235 (TYC 4384–1735–1, V ≈ 11.5 mag), whose transit signal was detected in the photometric time series of sectors 14, 20, and 21 of the TESS space mission. We confirm the planetary nature of the transit signal, which has a period of 3.44 d, by using precise RV measurements with the CARMENES, HARPS-N, and iSHELL spectrographs, supplemented by high-resolution imaging and ground-based photometry. A comparison of the properties derived for TOI-1235 b with theoretical models reveals that the planet has a rocky composition, with a bulk density slightly higher than that of Earth. In particular, we measure a mass of M(p) = 5.9 ± 0.6 Mꚛ and a radius of R(p) = 1.69 ± 0.08 Rꚛ, which together result in a density of ρp = 6.7(− 1.1,+ 1.3) g/cu. cm. When compared with other well-characterized exoplanetary systems, the particular combination of planetary radius and mass places our discovery in the radius gap, which is a transition region between rocky planets and planets with significant atmospheric envelopes. A few examples of planets occupying the radius gap are known to date. While the exact location of the radius gap for M dwarfs is still a matter of debate, our results constrain it to be located at around 1.7 Rꚛ or larger at the insolation levels received by TOI-1235 b (~60 Sꚛ). This makes it an extremely interesting object for further studies of planet formation and atmospheric evolution.

P. Bluhm↗
NASA NTRSDate not supplied

ISS External Microorganisms: A Payload to Close Planetary Protection Knowledge Gaps for Crewed Missions

Before NASA or COSPAR is able to set planetary protection requirements for crewed missions to locations like Mars there are a number of critical knowledge gaps that must be addressed (1). One of the most important knowledge gaps is an understanding of microbial leakage from crewed habitats and space suits. Current ECLSS (Environmental Control and Life Support System) and PLSS (Portable Life Support System) requirements do not include any provisions to control microbes that may escape along with vented or leaked gasses. The current generation of NASA space suits can leak at rates as high as 100 cm2 /min. during nominal operation (2). ISS (International Space Station) intentionally vents atmospheric gases like CO2 to maintain habitable conditions for the crew. Furthermore, every time an airlock is used for EVA (extravehicular activity)there is an accompanying release of internal atmosphere. Since it is not possible to sterilize a crewed mission, it is important that we understand what if any microbes are entrained in these vented and leaked products. It is also important to understand if these microbes can survive on exterior surfaces. Recent sampling of the Russian segments of ISS suggest that bacteria and fungi from inside ISS may be capable of surviving on external surfaces(3). NASA is developing an aseptic sampling tool for use during EVA and plans to collect samples from vents on ISS to build on these results. The results of this work will be used to develop planetary protection requirements for vented and leaked gasses from crewed volumes. NASA has developed and tested a tool kit for collecting microbiological samples during EVA(4). This tool kit contains eight commercially available, 23 mm. diameter, foam swabs that can be used to aseptically collect samples while at vacuum. The swabs are individually housed in aluminum canisters that are equipped with 0.2 μm Teflon filters. These filters allow the canisters to equilibrate to pressure changes while preventing microbiological contamination. The canisters will be cleaned and sterilized before flight. Results from ground-based testing indicate that this tool kit is capable of aseptically collecting microbes while at vacuum without becoming contaminated during pressure changes(5). Based on the results of this ground testing we have modified the tool kit to meet NASA safety requirements and improve the ergonomics. We added additional mounting points to the tool kit to give astronauts more options for securing it during use. We also changed the opening mechanism to improve the precision with which swabs can be extracted from the tool kit. We plan to use this kit on an upcoming EVA to collect samples from non-propulsive vents and areas near the U.S. airlock on ISS. These samples will be frozen at -80 ̊C and stored on station until they can be returned to Earth. We will analyze these returned samples using next generation DNA sequencing to determine the community composition and function of external ISS environments. The results of this study will close planetary protection knowledge gaps for crewed missions and will help NASA determine appropriate planetary protection requirements for life support systems. The tool kit will also be useful for collecting aseptic samples on upcoming crewed or robotic missions and could easily be modified to collect samples with organic contamination control requirements as well.

A B Regberg↗
NASA NTRSDate not supplied

ISS External Microorganisms: A Payload to Close Planetary Protection Knowledge Gaps for Crewed Missions

Before NASA or COSPAR is able to set planetary protection requirements for crewed missions to locations like Mars there are a number of critical knowledge gaps that must be addressed (1). One of the most important knowledge gaps is an understanding of microbial leakage from crewed habitats and space suits. Current ECLSS (Environmental Control and Life Support System) and PLSS (Portable Life Support System) requirements do not include any provisions to control microbes that may escape along with vented or leaked gasses. The current generation of NASA space suits can leak at rates as high as 100 cm2 /min. during nominal operation (2). ISS (International Space Station) intentionally vents atmospheric gases like CO2 to maintain habitable conditions for the crew. Furthermore, every time an airlock is used for EVA (extravehicular activity)there is an accompanying release of internal atmosphere. Since it is not possible to sterilize a crewed mission, it is important that we understand what if any microbes are entrained in these vented and leaked products. It is also important to understand if these microbes can survive on exterior surfaces. Recent sampling of the Russian segments of ISS suggest that bacteria and fungi from inside ISS may be capable of surviving on external surfaces(3). NASA is developing an aseptic sampling tool for use during EVA and plans to collect samples from vents on ISS to build on these results. The results of this work will be used to develop planetary protection requirements for vented and leaked gasses from crewed volumes. NASA has developed and tested a tool kit for collecting microbiological samples during EVA(4). This tool kit contains eight commercially available, 23 mm. diameter, foam swabs that can be used to aseptically collect samples while at vacuum. The swabs are individually housed in aluminum canisters that are equipped with 0.2 μm Teflon filters. These filters allow the canisters to equilibrate to pressure changes while preventing microbiological contamination. The canisters will be cleaned and sterilized before flight. Results from ground-based testing indicate that this tool kit is capable of aseptically collecting microbes while at vacuum without becoming contaminated during pressure changes(5). Based on the results of this ground testing we have modified the tool kit to meet NASA safety requirements and improve the ergonomics. We added additional mounting points to the tool kit to give astronauts more options for securing it during use. We also changed the opening mechanism to improve the precision with which swabs can be extracted from the tool kit. We plan to use this kit on an upcoming EVA to collect samples from non-propulsive vents and areas near the U.S. airlock on ISS. These samples will be frozen at -80 ̊C and stored on station until they can be returned to Earth. We will analyze these returned samples using next generation DNA sequencing to determine the community composition and function of external ISS environments. The results of this study will close planetary protection knowledge gaps for crewed missions and will help NASA determine appropriate planetary protection requirements for life support systems. The tool kit will also be useful for collecting aseptic samples on upcoming crewed or robotic missions and could easily be modified to collect samples with organic contamination control requirements as well.

A B Regberg↗
NASA NTRSDate not supplied

Final Report of the COSPAR Meeting Series on Knowledge Gaps in Planetary Protection for Crewed Missions to Mars

The international scientific community has, through a Committee on Space Research (COSPAR) meeting series, participated in a seven-year review of knowledge gaps in planetary protection for crewed missions to Mars. This meeting series first identified a prioritized list of knowledge gaps that, if addressed, would permit development of an implementable planetary protection policy for the initial crewed Mars mission. Next, a consideration of the available venues (ground, LEO, deep space, planetary surfaces) yielded a roadmap of potential future investigations needed to close the knowledge gaps. Finally, the meeting series evaluated topic-specific measurements that are essential to establishing the figures of merit needed for hardware engineering design requirements. The three main topic threads considered within the meeting series were: microbial and human health monitoring; natural transport of terrestrial biological contamination on Mars, and; technologies and operations for contamination control (of spacecraft systems). Participants at the meeting series included engineers, scientists, managers and various subject matter experts from space agencies, academic and research institutions, commercial companies, and other government departments. This paper provides a detailed summary review of the findings of the meeting series, including descriptions of the basis for each of the figures of merit (where they were identified), and considerations of how planetary protection implementation and policy for crewed missions may progress from the current state of the art.

J Andy Spry↗
NASA NTRSDate not supplied

Space Crop Production Gaps and Challenges

As astronauts venture farther from Earth, and stay for longer periods, the space food system will increase in importance. Crop production can supplement a pre-packaged space diet to provide nutrition and dietary variety for space crews. In future missions, bioregenerative approaches may be used to generate a larger percentage of the diet, as well as help to reduce life support system burdens and resupply from Earth. Plants may also provide behavioral health benefits to crew members living in the isolated, confined environment of a space habitat. A number of unique challenges exist for growth of plants in microgravity and on other reduced gravity surfaces like the moon and Mars. Testing plant growth inside the Veggie and Advanced Plant Habitat (APH) chambers on the International Space Station is allowing us to understand the impacts of gravity and spaceflight on crop growth, nutritional content, acceptability, and the importance of plants to astronauts living and working away from Earth. We are also gaining a better understanding of food safety concerns and the behavior of space plant microbiomes and plant pathogens, but major gaps in knowledge remain. As we move from research towards operational space crop production to enable exploration, there are numerous gaps in technology, knowledge, and practice related to space crop growth that must be addressed. Research and development in key focus areas such as effective water and nutrient delivery at variable gravity levels, autonomous plant health monitoring, growth system cleaning and disinfection, and selection of ideal space crops are needed to fill these gaps. Breeding or engineering custom space crops may impact areas including plant growth and development, plant physiology, produce nutrition, organoleptic acceptability, and post-harvest characteristics, and these may further enable space crop production scenarios. Space crop challenges are multifaceted and require diverse interdisciplinary teams working together to develop effective solutions. Solving these requires an array of skill sets from across the biological and physical sciences, engineering, and human social sciences. Solutions to help ensure food security off-Earth may also translate to more sustainable terrestrial crop production approaches, and regular dialog between industry, academia, and government organizations working in related fields benefit all. Additional help can come from engagement with student researchers at various levels through courses, participatory science projects, and open science activities which can provide useful data. Global coordination and integration between space agencies and partners will be essential.

Gioia Donna Massa↗
NASA NTRSDate not supplied

Space Crop Production Gaps and Challenges

As astronauts venture farther from Earth, and stay for longer periods, the space food system will increase in importance. Crop production can supplement a pre-packaged space diet to provide nutrition and dietary variety for space crews. In future missions, bioregenerative approaches may be used to generate a larger percentage of the diet, as well as help to reduce life support system burdens and resupply from Earth. Plants may also provide behavioral health benefits to crew members living in the isolated, confined environment of a space habitat. A number of unique challenges exist for growth of plants in microgravity and on other reduced gravity surfaces like the moon and Mars. Testing plant growth inside the Veggie and Advanced Plant Habitat (APH) chambers on the International Space Station is allowing us to understand the impacts of gravity and spaceflight on crop growth, nutritional content, acceptability, and the importance of plants to astronauts living and working away from Earth. We are also gaining a better understanding of food safety concerns and the behavior of space plant microbiomes and plant pathogens, but major gaps in knowledge remain. As we move from research towards operational space crop production to enable exploration, there are numerous gaps in technology, knowledge, and practice related to space crop growth that must be addressed. Research and development in key focus areas such as effective water and nutrient delivery at variable gravity levels, autonomous plant health monitoring, growth system cleaning and disinfection, and selection of ideal space crops are needed to fill these gaps. Breeding or engineering custom space crops may impact areas including plant growth and development, plant physiology, produce nutrition, organoleptic acceptability, and post-harvest characteristics, and these may further enable space crop production scenarios. Space crop challenges are multifaceted and require diverse interdisciplinary teams working together to develop effective solutions. Solving these requires an array of skill sets from across the biological and physical sciences, engineering, and human social sciences. Solutions to help ensure food security off-Earth may also translate to more sustainable terrestrial crop production approaches, and regular dialog between industry, academia, and government organizations working in related fields benefit all. Additional help can come from engagement with student researchers at various levels through courses, participatory science projects, and open science activities which can provide useful data. Global coordination and integration between space agencies and partners will be essential.

Gioia Massa↗
NASA NTRS2024

Volatiles in melt inclusions from lunar mare basalts: Bridging the gap in the H 2 O/Ce ratio between melt Inclusions in lunar pyroclastic sample 74220 and other mare samples

The H2O concentration and H 2 O/Ce ratio in olivine-hosted melt inclusions are high in lunar pyroclastic sample 74220 (H 2 O up to 1410 ppmw; H 2 O/Ce up to 77) but lower (H2O 10 to 430 ppmw; H 2 O/Ce 0.3 to 9.4) in all other lunar samples studied before this work. The difference in H 2 O concentration and in H 2 O/Ce ratio is absent for other volatile elements (F, S, and Cl) in melt inclusions in 74220 and other lunar samples. Because H 2 O (or H) is a critical volatile component with significant ramifications on the origin and evolution of the Moon, it is important to understand what causes such a large gap in H 2 O/Ce ratio between 74220 and other lunar samples. Two explanations have been advanced. One is that volcanic product in sample 74220 has the highest cooling rate and thus best preserved H 2 O in melt inclusions compared to melt inclusions in other samples. The other explanation is that sample 74220 comes from a localized heterogeneity enriched in some volatiles. To distinguish these two possibilities, here we present new data from two rapidly cooled lunar samples with glassy melt inclusions: olivine-hosted melt inclusions (OHMIs) in 79135 regolith breccia (unknown cooling rate but with glassy MIs similar in texture with those in 74220), and pyroxene-hosted melt inclusions (PHMIs) in 15597 pigeonite basalts (known high cooling rate, second only to 74220 and 15421). In addition, we also investigated new OHMIs in sample 74220. If the gap is due to the difference in cooling rates, samples with cooling rates between those of 74220 and other studied lunar samples should have preserved intermediate H2O concentrations and H 2 O/Ce ratios. Our results show that melt inclusions in 79135 and 15597 contain high H 2 O concentrations (up to 969 ppmw in 79135 and up to 793 ppmw in 15597) and high H 2 O/Ce ratios (up to 21 in 79135 and up to 13 in 15997), bridging the big gap in H 2 O/Ce ratio among 74220 and other lunar samples. Combined with literature data, we confirm that H 2 O/Ce ratios of different lunar samples are positively correlated to the cooling rates and independent of the type of mare basalts. We hence reinforce the interpretation that the lunar sample with the highest cooling rate best represents pre-eruptive volatiles in lunar basalts due to the least degassing. Based on Ce concentration in the primitive lunar mantle, we estimate that H 2 O concentration in the primitive lunar mantle (meaning bulk silicate Moon) is 121 ± 15 ppmw. Our new data also further constrain F/P, S/Dy and Cl/Ba ratios in lunar basalts and the lunar mantle. Estimated F, P, and S concentrations in the lunar primitive mantle are 4.4 ± 1.1 ppmw, 22 ± 8 ppmw, and 67 +67 −33 ppmw, respectively.

Xue Su↗
DOE OSTI2021

Gap Assessment on Sensors and Instrumentation for Advanced Reactors

The Sensor Technologies for Advanced Reactors Virtual Workshop—sponsored by the Gateway for Accelerated Innovation in Nuclear (GAIN), the Electric Power Research Institute, and the Nuclear Energy Institute—was held to exchange information on sensors and sensor technologies of interest to advanced nuclear technology developers, commercial instrument suppliers, and sensor researchers from Department of Energy (DOE) national laboratories, universities, and industry. The workshop objectives were to discuss measurement requirements and sensor needs for advanced reactor concepts, understand current national laboratory capabilities and accelerated development approaches for sensors and instrumentation, and identify gaps so as to inform applicable DOE Office of Nuclear Energy (DOE-NE) research programs. Due to the complexity of holding group discussions on individual gaps, a survey was sent to workshop participants, and personalized one-on-one feedback sessions were held to elicit additional information. Summaries of these sessions are provided in this gap assessment report.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Variable gap thermal conductivity apparatus and method

An apparatus and a method for determining the thermal conductivity of a fluid specimen are provided. The apparatus and the method include determining thermal conductivity using a quasi-steady state variable gap axial flow technique. The fluid specimen is heated on one side by a heat source with a known power output and cooled on the other side. After reaching steady state, a resulting temperature drop through the fluid specimen exists. This temperature drop, the known fluid specimen thickness (or gap distance), and the known power output are used to calculate the thermal resistance of the fluid specimen. The thermal conductivity of the fluid specimen is then determined using a curve fit of thermal resistance with respect to gap distance.

Gallagher, Ryan C.↗
DOE OSTI2026

The General Antiparticle Spectrometer (GAPS) Antarctic Balloon Payload

The General Antiparticle Spectrometer (GAPS) is an Antarctic stratospheric balloon mission designed to provide unmatched sensitivity to low-energy (<0.25 GeV/n) cosmic-ray antiprotons, antideuterons, and antihelium nuclei as signatures of dark matter. The distinctive GAPS particle identification technique relies on measuring the energy loss along the track of an incoming antinucleus as it slows down and is captured into an exotic atom, and then detecting the de-excitation X-rays and the nuclear annihilation products. This measurement is realized using a Tracker composed of more than 1000 custom silicon strip detectors and a plastic scintillator time-of-flight (TOF) system instrumenting more than 40m$^2$. Together, these subsystems provide the velocity and energy resolution, stopping power, particle tracking, and X-ray identification necessary to distinguish rare antinucleus signals from the abundant positive-nucleus backgrounds, all within the constraints of a high-altitude mission. A multi-loop capillary heat pipe system has been developed to maintain the tracker operating temperature with significant mass and power savings over a conventional pump-based system. The first GAPS science payload flew for 25 days during the 2025/26 NASA Antarctic balloon campaign. We detail the design, integration, and commissioning of the payload prior to flight.

Aoyama, Kazutaka [JAXA, Sagamihara]↗
DOE OSTI2020

NRIC Gap Assessment

The National Reactor Innovation Center (NRIC) conducted a Gap Assessment to identify the missing national laboratory capabilities needed to enable demonstration of industry reactor concepts. Input was gathered from the NRIC Demonstration Reactor Capabilities Survey (DRCS), experience with the DE-FOA-0002271 “Advanced Reactor Demonstration” proposal development process, and industry-led Technology Working Group (TWG) letters. Thirty-seven reactor concepts from industry were considered in the Gap Assessment and 20 fundamental problems were identified.

42 ENGINEERING↗
DOE OSTI2020

High-Temperature Nucleation of GaP on V-Grooved Si

The use of nanopatterned {111}-faceted v-grooves has recently shown promise for growing high-quality III–V material on Si. Here, we study the effect of reactor conditions and surface pretreatments on the nucleation of GaP on v-grooved Si in a high-temperature regime, which offers the promise of a defect-free GaP/Si interface favorable for Si passivation and dislocation glide in the GaP. X-ray photoelectron spectroscopy was used to understand the Si surface chemistry prior to nucleation, and transmission electron microscopy was used to probe material quality of the nuclei. Temperature and V/III ratio were found to control the facet selectivity of nucleation. We demonstrate a condition of high temperature and high V–III ratio that leads to uniform nucleation at the bottom of the trenches, with initial material free of nucleation-related interfacial defects. This optimized condition was then shown to coalesce into a thin film after additional growth.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Engineering Small HOMO–LUMO Gaps in Polycyclic Aromatic Hydrocarbons with Topologically Protected States

Topological phases in laterally confined low-dimensional nanographenes have emerged as versatile design tools that can imbue otherwise unremarkable materials with exotic band structures ranging from topological semiconductors and quantum dots to intrinsically metallic bands. The periodic boundary conditions that define the topology of a given lattice have thus far prevented the translation of this technology to the quasi-zero-dimensional (0D) domain of small molecular structures. Here, we describe the synthesis of a polycyclic aromatic hydrocarbon (PAH) featuring two localized zero modes (ZMs) formed by the topological junction interface between a trivial and nontrivial phase within a single molecule. First-principles density functional theory calculations predict a strong hybridization between adjacent ZMs that gives rise to an exceptionally small HOMO–LUMO gap. Scanning tunneling microscopy and spectroscopy corroborate the molecular structure of 9/7/9-double quantum dots and reveal an experimental quasiparticle gap of 0.16 eV, corresponding to a carbon-based small molecule long-wavelength infrared (LWIR) absorber.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Dynamic Tuning of Gap Plasmon Resonances Using a Solid-State Electrochromic Device

Plasmonic antennas and metasurfaces can effectively control light–matter interactions, and this facilitates a deterministic design of optical materials properties, including structural color. However, these optical properties are generally fixed after synthesis and fabrication, while many modern-day optics applications require active, low-power, and nonvolatile tuning. These needs have spurred broad research activities aimed at identifying materials and resonant structures capable of achieving large, dynamic changes in optical properties, especially in the challenging visible spectral range. In this work, we demonstrate dynamic tuning of polarization-dependent gap plasmon resonators that contain the electrochromic oxide WO 3 . Its refractive index in the visible changes continuously from n = 2.1 to 1.9 upon electrochemical lithium insertion and removal in a solid-state device. By incorporating WO 3 into a gap plasmon resonator, the resonant wavelength can be shifted continuously and reversibly by up to 58 nm with less than 2 V electrochemical bias voltage. Lastly, the resonator can remain in a tuned state for tens of minutes under open circuit conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Momentum-resolved superconducting energy gaps of Sr 2 RuO 4 from quasiparticle interference imaging

Sr 2 RuO 4 has long been the focus of intense research interest because of conjectures that it is a correlated topological superconductor. It is the momentum space ( k -space) structure of the superconducting energy gap Δ i ( k ) on each band i that encodes its unknown superconducting order parameter. However, because the energy scales are so low, it has never been possible to directly measure the Δ i ( k ) of Sr 2 RuO 4 . In this work, we implement Bogoliubov quasiparticle interference (BQPI) imaging, a technique capable of high-precision measurement of multiband Δ i ( k ). At T = 90 mK,we visualize a set of Bogoliubov scattering interference wave-vectors q j : j = 1 – 5 consistent with eight gap nodes/minima that are all closely aligned to the (±1, ±1) crystal lattice directions on both the α and β bands. Taking these observations in combination with other very recent advances in directional thermal conductivity, temperature-dependent Knight shift, time-reversal symmetry conservation, and theory, the BQPI signature of Sr 2 RuO 4 appears most consistent with Δ i ( k ) having d x 2 – y 2 ( B 1 g ) symmetry.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Mono- and bilayer smectic liquid crystal ordering in dense solutions of “gapped” DNA duplexes

Significance Liquid crystalline behavior of DNA has been studied for decades, yet only recently has one of the most fundamental liquid crystal phases—the smectic phase in which rod-like objects assemble into stacks of fluid layers—been demonstrated in this system. Here, we describe distinct bilayer and monolayer smectic phases in solutions of “gapped” DNA (GDNA), consisting of two DNA duplexes connected by a single strand. The smectic order is amphotropic (sensitive to temperature as well as concentration), and the layer structure is stable against significant perturbations of the GDNA construct (e.g., “gap” length variation and asymmetry in duplex lengths). The temperature sensitivity may provide a means to compare end-to-end interaction strengths between DNA duplexes at biologically relevant concentrations.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Changes of deformed shell gaps at N ~ 100 in light rare-earth, neutron-rich nuclei

There have been compelling evidences indicating that deformed single-particle states in neutron- rich regions are different from those in the stable region. It was pointed out that for the light rare- earth (60Nd, 62Sm, and 64Gd), neutron-rich (N = 98-102) nuclei, the Woods-Saxon potential, the Nilsson modified oscillator potential with "universal" parameters, and the folded Yukawa potential all failed to describe the correct ordering of neutron single-particle states. The location and size of deformed shell gaps in this mass region are under current debate. We propose a modification for the "standard" Nilsson parameters of Bengtsson and Ragnarsson introduced in 1985. The proposed N-dependent spin-orbit interaction brings an effect of the tensor force for the deformed potential, which causes dynamic changes in deformed shell gaps with neutron number and deformation. By applying the modified Nilsson parameters to generate deformed bases for the Projected Shell Model, we demonstrate that the calculation can explain consistently the current experimental data, including the ground state configuration in odd-neutron nuclei, upbending of the yrast moment of inertia at higher spins and the energies of 2-quasineutron 6- and 4- isomers in even-even nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Specific heat and gap structure of a nematic superconductor: Application to FeSe

We report the results of our in-depth analysis of spectroscopic and thermodynamic properties of a multiorbital metal, like FeSe, which first develops a nematic order and then undergoes a transition into a superconducting state, which coexists with nematicity. We analyze the angular dependence of the gap function and specific heat C v (T) of such a nematic superconductor. We specifically address three issues: (i) the angular dependence of the gap in light of the competition between the nematicity-induced s - d mixture and the orbital transmutation of low-energy excitations in the nematic state, (ii) the effect of nematicity on the magnitude of the jump of the specific heat C v (T) at T c and the temperature dependence of C v (T) below T c , and (iii) a potential transition at T c1 < T c from an s + d state to an s + e iη d state that breaks time-reversal symmetry. We consider two scenarios for a nematic order: scenario A, in which this order develops between d xz and d yz orbitals on hole and electron pockets, and scenario B, in which there is an additional component of the nematic order for d xy fermions on the two electron pockets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗