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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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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Time, momentum, and energy resolved pump-probe tunneling spectroscopy of two-dimensional electron systems

Abstract Real-time probing of electrons can uncover intricate relaxation mechanisms and many-body interactions in strongly correlated materials. Here, we introduce time, momentum, and energy resolved pump-probe tunneling spectroscopy (Tr-MERTS). The method allows the injection of electrons at a particular energy and observation of their subsequent decay in energy-momentum space. Using Tr-MERTS, we visualize electronic decay processes, with lifetimes from tens of nanoseconds to tens of microseconds, in Landau levels formed in a GaAs quantum well. Although most observed features agree with simple energy-relaxation, we discovered a splitting in the nonequilibrium energy spectrum in the vicinity of a ferromagnetic state. An exact diagonalization study suggests that the splitting arises from a maximally spin-polarized state with higher energy than a conventional equilibrium skyrmion. Furthermore, we observe time-dependent relaxation of the splitting, which we attribute to single-flipped spins forming skyrmions. These results establish Tr-MERTS as a powerful tool for studying the properties of a 2DES beyond equilibrium.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Weak links in proximity-superconducting two-dimensional electron systems

Here, we find a giant inverse proximity effect that arises in small low-dimensional superconductor-normal-superconductor (S/N/S) junctions, where a proximity coherence length is larger than the coherence length of a source superconductor, due to a huge backaction exerted by normal conductors on the proximity superconducting regions. Furthermore, the inverse proximity develops even in case where dimensions of the normal parts are smaller than the proximity coherence length and significantly suppresses superconducting characteristics of the entire system, including critical current, well below those for the usual S/N/S structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

LaTiO{sub 3}/KTaO{sub 3} interfaces: A new two-dimensional electron gas system

We report a new 2D electron gas (2DEG) system at the interface between a Mott insulator, LaTiO{sub 3}, and a band insulator, KTaO{sub 3}. For LaTiO{sub 3}/KTaO{sub 3} interfaces, we observe metallic conduction from 2 K to 300 K. One serious technological limitation of SrTiO{sub 3}-based conducting oxide interfaces for electronics applications is the relatively low carrier mobility (0.5-10 cm{sup 2}/V s) of SrTiO{sub 3} at room temperature. By using KTaO{sub 3}, we achieve mobilities in LaTiO{sub 3}/KTaO{sub 3} interfaces as high as 21 cm{sup 2}/V s at room temperature, over a factor of 3 higher than observed in doped bulk SrTiO{sub 3}. By density functional theory, we attribute the higher mobility in KTaO{sub 3} 2DEGs to the smaller effective mass for electrons in KTaO{sub 3}.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Suppression of electron magnetotunneling between parallel two-dimensional GaAs/InAs electron systems by the correlation interaction

Magnetotunneling between two-dimensional GaAs/InAs electron systems in vertical resonant tunneling GaAs/InAs/AlAs heterostructures is studied. A new-type of singularity in the tunneling density of states, specifically a dip at the Fermi level, is found; this feature is drastically different from that observed previously for the case of tunneling between two-dimensional GaAs tunnel systems in terms of both the kind of functional dependence and the energy and temperature parameters. As before, this effect manifests itself in the suppression of resonant tunneling in a narrow range near zero bias voltage in a high magnetic field parallel to the current direction. Magnetic-field and temperature dependences of the effect's parameters are obtained; these dependences are compared with available theoretical and experimental data. The observed effect can be caused by a high degree of disorder in two-dimensional correlated electron systems as a result of the introduction of structurally imperfect strained InAs layers.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Electrical generation and detection of spin waves in a quantum Hall ferromagnet

Spin waves are collective excitations of magnetic systems. An attractive setting for studying long-lived spin-wave physics is the quantum Hall (QH) ferromagnet, which forms spontaneously in clean two-dimensional electron systems at low temperature and in a perpendicular magnetic field. We used out-of-equilibrium occupation of QH edge channels in graphene to excite and detect spin waves in magnetically ordered QH states. Our experiments provide direct evidence for long-distance spin-wave propagation through different ferromagnetic phases in the N = 0 Landau level, as well as across the insulating canted antiferromagnetic phase. Our results will enable experimental investigation of the fundamental magnetic properties of these exotic two-dimensional electron systems.

Science & Technology - Other Topics↗