Long-mean-free-path ballistic hot electrons in high-purity GaAs

Electronic transport in Fermi liquids is usually Ohmic, because of momentum-relaxing scattering due to defects and phonons. These processes can become sufficiently weak in two-dimensional materials, giving rise to either ballistic or hydrodynamic transport, depending on the strength of electron-electron scattering. We show that the ballistic regime is a quantum critical point (QCP) on the regime boundary separating Ohmic and hydrodynamic transport. The QCP corresponds to a free conformal field theory (CFT) with a dynamical scaling exponent z = 1. Its nontrivial aspects emerge in device geometries with shear, wherein the regime has an intrinsic universal dissipation, a nonlocal current-voltage relation, and exhibits the critical scaling of the underlying CFT. The Fermi surface has electron-hole pockets across all angular scales and the current flow has vortices at all spatial scales. We image the fluctuations in high-definition and animate their emergence as experimental parameters are tuned to the QCP a . The vortices clearly demonstrate that Pauli exclusion alone can produce collective effects, with low-frequency AC transport mediated by vortex dynamics b . The scale-invariant spatial structure is much richer than that of an interaction-dominated hydrodynamic regime, which only has a single vortex at the device scale. Our findings provide a theoretical framework for both interaction-free and interaction-dominated non-Ohmic transport in two-dimensional materials, as seen in several contemporary experiments. a Spatial fluctuations: https://vimeo.com/365020115 , Fermi surface fluctuations: https://vimeo.com/ 364982637 b Vortex dynamics and frequency crossover: https://vimeo.com/366725650Quantum critical points (QCP) mediate second-order quantum phase transitions (QPT), produced by tuning non-thermal parameters such as doping, magnetic field or pressure. Systems at QCPs obey universal scaling, and are dominated by quantum fluctuations [1]. A prototypical QPT occurs in the 1D quantum Ising model in a transverse magnetic field, realized in CoNb 2 O 6 [2]. As the external field is increased, the ground state changes from an ordered phase set by exchange interaction to a field-aligned quantum paramagnet. The transition occurs through a QCP with a dynamical scaling exponent z = 1, which connects the correlation length ξ and time τ via τ ∝ ξ z . Remarkably, the ubiquitous Fermi liquid hosts exactly such a QCP in the form of free fermions; a Fermi gas. Absent all interactions, gapless quasiparticles on the Fermi surface obey a relativistic free-field conformal field theory (CFT), with the speed of light set by the Fermi velocity v F [3]. This simple CFT exhibits critical scaling with z = 1. Microscopic interactions are indeed irrelevant, as expected at criticality, because there are none.Although a Fermi gas obeys critical scaling [4], it is never pictured as a QCP. The singleparticle Green's function has a simple pole, not a branch cut characteristic of interacting QCPs [5]; it is unclear how and where critical fluctuatio...

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“…These requirements have already been achieved. Examples include graphene/hBN [20][21][22], and GaAs [23].…”

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confidence: 99%

Hydrodynamic and ballistic AC transport in two-dimensional Fermi liquids

et al. 2019

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“…In order to get transmission enhancement by two layers, electron propagation between the layers should be ballistic. Therefore, we consider the separation of the layers L = 80 nm, which is comparable to the mean free path of the electrons in GaAs/AlGaAs superlattices 61 and considerably smaller compared to pure GaAs samples 62 . We take the electron energy to be 20 meV for which case kr eff ≪ 1 (r eff is estimated using the Van der Waals length~0.2 nm), allowing us to apply the theory developed in this paper.…”

Section: Discussionmentioning

confidence: 99%

Filtering spins by scattering from a lattice of point magnets

2020

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Nature creates electrons with two values of the spin projection quantum number. In certain applications, it is important to filter electrons with one spin projection from the rest. Such filtering is not trivial, since spin-dependent interactions are often weak, and cannot lead to any substantial effect. Here we propose an efficient spin filter based upon scattering from a two-dimensional crystal, which is made of aligned point magnets. The polarization of the outgoing electron flux is controlled by the crystal, and reaches maximum at specific values of the parameters. In our scheme, polarization increase is accompanied by higher reflectivity of the crystal. High transmission is feasible in scattering from a quantum cavity made of two crystals. Our findings can be used for studies of low-energy spin-dependent scattering from two-dimensional ordered structures made of magnetic atoms or aligned chiral molecules.

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“…Определение этой величины является нетривиальной задачей и выходит за рамки настоящей работы. Отметим только, что в работе [54] было показано, что в достаточно чистых образцах GaAs при температуре жидкого гелия величина l может достигать 3 µm. При таком значении среднего свободного пробега электрона условие (14) не выполняется для всех рассмотренных нами значений L, и полученные выше результаты остаются в силе.…”

Section: результаты и обсуждениеunclassified

Зависимость Светоэкситонного Взаимодействия От Ширины Квантовой Ямы Во Внешнем Однородном Электрическом Поле

Логинов¹,

Донец²

2021

Физика Твердого Тела

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The paper is devoted to analyse of the dependance of exciton-light coupling on a quantum well thickness at presence of an uniform electric field. It is shown that the increasing of quantum well thickness at an enough strong field results in decreasing of the exciton-light coupling in compare with narrower wells.The numerical calculations of longitudinal-transverse splitting are performed for a wide ranges of both electric field and values of quantum well thickness.The analyse of obtained data allows to get analytical expressions which desсribe the exciton-light coupling dependence like on the electric field as quantum well thickness.

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Long-mean-free-path ballistic hot electrons in high-purity GaAs

Cited by 17 publications

References 6 publications

Hydrodynamic and ballistic AC transport in two-dimensional Fermi liquids

Hydrodynamic and ballistic AC transport in two-dimensional Fermi liquids

Filtering spins by scattering from a lattice of point magnets

Зависимость Светоэкситонного Взаимодействия От Ширины Квантовой Ямы Во Внешнем Однородном Электрическом Поле

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