Electron Gas System Research Articles

Modified Martin-Puplett interferometer for magneto-optical Kerr effect measurements at sub-THz frequencies.

We present a magneto-optical Kerr effect (MOKE) spectrometer based on a modified Martin-Puplett interferometer, utilizing continuous wave sub-THz low-power radiation in a broad frequency range. This spectrometer is capable of measuring the frequency dependence of the MOKE response function, both the Kerr rotation and ellipticity, simultaneously, with accuracy limited by a sub-milliradian threshold, without the need for a reference measurement. The instrument's versatility allows it to be coupled to a cryostat with optical windows, enabling studies of a variety of quantum materials such as unconventional superconductors, two-dimensional electron gas systems, quantum magnets, and other systems showing optical Hall response at sub-Kelvin temperatures and in high magnetic fields. We demonstrate the functionality of the MOKE spectrometer using an undoped InSb wafer as a test sample.

Non-classical correlations and coherence in a two-dimensional electron gas under the influence of Rashba spin–orbit coupling

This investigation delves into the dynamics of quantum correlations and coherence within a two-dimensional electron gas (2DEG) system, taking into account the influence of Rashba spin–orbit coupling (SOC). We utilize metrics such as logarithmic negativity ([Formula: see text]), local quantum uncertainty (LQU ([Formula: see text])), and relative entropy of coherence ([Formula: see text]) to specifically assess these quantum resources among electron spins within non-interacting electron gases. Our study investigates how the separation distance (R) between electrons and the intensity of Rashba SOC ([Formula: see text]), impact the behavior of quantum properties within the 2DEG system. We find that specific strengths of Rashba SOC can effectively regulate quantum correlations and coherence within this system. Particularly significant is our observation that optimal quantum indicators emerge when electron proximity is minimized, underscoring the substantial influence of electron distance on quantum characteristics. Conversely, as electron separation increases, these quantum metrics diminish. Therefore, by adjusting the Rashba parameter, we can enhance the resilience of these quantum measurements against increasing electron separations, providing valuable insights into the potential for controlling and manipulating quantum behavior in similar 2DEG systems.

Plasmonic Photovoltaic Effect of an Original 2D Electron Gas System and Application in Mid‐Infrared Imaging

AbstractOwing to their consistently emerging applications in modern photonics, highly sensitive and rapid mid‐infrared (MIR) photodetectors, operating at high temperatures, are of great significance. Herein, a novel PbTe/Ge heterostructure is introduced. Notably, the discovery of a 2D electron gas (2DEG) system on the surface of the PbTe layer is experimentally identified for the first time. A high‐performance PbTe/Ge heterostructure MIR photodetector utilizing a plasmonic photovoltaic effect is developed by employing asymmetric electrodes. The photodetecting device demonstrates an exceptionally high detectivity of 1.1 × 1011 Jones along with a short response time of 15 ns at room temperature. Additionally, the proposed plasmonic photovoltaic mechanism of the device is investigated and mainly ascribed to the propagating plasmons, generated by the coupling of the 2DEG with incident MIR photons. Moreover, a linear detector array (LDA) of PbTe/Ge is demonstrated for a thermal imaging application, which exhibits promising high‐quality real‐time imaging via the 2D photodetector arrays on Ge‐based integrated circuits. This work opens up a new way for the development of next‐generation, advanced MIR photonic devices and integrated photonic systems.

Degeneracy pressure in the presence of maximum length for non-interacting electrons

Combining quantum theory with the fundamental principles of gravity results in the modification of the uncertainty principle. In this study, we employ the extended uncertainty principle (EUP) with the maximum length derived from the cosmological particle horizon. The impact of this specific kind of modification is examined in a non-interacting electron gas system. We analytically derive the generalized relations for the degeneracy pressure and the bulk modulus. An intriguing finding is that the degeneracy pressure is reduced, as confirmed by the observed size of white dwarfs, which is smaller than what is predicted by the standard theory. Nevertheless, it is still capable of providing support against gravitational collapse.

Anomalous enhancement of thermoelectric power factor in multiple two-dimensional electron gas system.

Toward drastic enhancement of thermoelectric power factor, quantum confinement effect proposed by Hicks and Dresselhaus has intrigued a lot of researchers. There has been much effort to increase power factor using step-like density-of-states in two-dimensional electron gas (2DEG) system. Here, we pay attention to another effect caused by confining electrons spatially along one-dimensional direction: multiplied 2DEG effect, where multiple discrete subbands contribute to electrical conduction, resulting in high Seebeck coefficient. The power factor of multiple 2DEG in GaAs reaches the ultrahigh value of ~100 μWcm-1 K-2 at 300 K. We evaluate the enhancement rate defined as power factor of 2DEG divided by that of three-dimensional bulk. The experimental enhancement rate relative to the theoretical one of conventional 2DEG reaches anomalously high (~4) in multiple 2DEG compared with those in various conventional 2DEG systems (~1). This proposed methodology for power factor enhancement opens the next era of thermoelectric research.

Polarization-selective equilibration and quantum interference in graphene-based quantum Hall edge states

Quantum Hall (QH) edge states in two-dimensional electron gas systems have drawn attention as potential carriers of quantum information, owing to their chiral ballistic nature, arising from Landau level formation under a strong perpendicular magnetic field. They remain stable even in the presence of material disorder, making them ideal for phase-sensitive measurements like QH interferometry. We report the equilibration processes between electron waves in spin and valley polarized QH edge states, particularly in a four-terminal measurement configuration. We compare experimental results with theoretical estimations based on the Landauer formula, taking into account selective equilibration depending on spin polarization. Furthermore, quantum interference in co-propagating QH edge states is investigated, elucidating how factors such as magnetic fields, voltage bias, and gate configurations influence quantum phase. The research offers insights into the controllability of interactions between QH edge states, vital for harnessing the potential of graphene in QH interferometers and quantum information processing.

Highly directional and carrier density-independent plasmons in quasi-one-dimensional electron gas systems

Recent advancements in developing metahyperbolic surfaces through substrate patterning have enabled the realization of highly-directional hyperbolic surface plasmons, but the feasibility of reproducing the same properties in natural hyperbolic two-dimensional (2D) materials is still unexplored. In this study, we expand the possibility of natural 2D materials in achieving electromagnetic scenarios akin to those observed in metahyperbolic surfaces. Natural hyperbolic 2D materials provide inherent advantages for simplicity, predictability, and lower losses compared to meta-surfaces. By employing first-principles calculations, we find that realistic 2D material, specifically the RuOCl2 monolayer, are suitable alternatives to metahyperbolic surfaces. Indeed, RuOCl2 monolayer sustains carrier-density-independent and broadband low-loss hyperbolic responses across the terahertz to ultraviolet spectral range, owning to the highly-anisotropic electronic band structures characterized by quasi-one-dimensional electron gas. These findings shed light on the integration of hyperbolicity in natural 2D materials, opening new avenues for the design and development of optoelectronic devices and nanoscale imaging systems.

Tunneling conductance regulated by the electrostatic barrier in monolayer black phosphorene

We investigate the tunneling conductance of monolayer black phosphorene through double magnetic barriers modulated by the electrostatic barrier. This magnetic barrier is generated by two ferromagnetic strips deposited on monolayer phosphorene and can form parallel (P) and antiparallel (AP) structures. Applying a voltage to a ferromagnetic strip will create an electrostatic barrier. The transmission of P and AP magnetic structures is calculated using the transfer matrix. Tunneling conductance is given by Landauer–Büttiker theory. Our results show that under double electrostatic barriers modulation, the AP conductance of the system is zero except for sharp peaks, while the P conductance has a certain value, which implies a large tunneling magnetoresistance. However, in the case of single electrostatic barrier modulation, the conductance becomes flat. For the Fermi level in the valence band, the movement of the Fermi level leads to the severe mismatching of transmitted wave vectors in the barrier region, resulting a positive and negative oscillation magnetoresistance. This may be useful for designing memory using a two-dimensional electron gas system.

Control over epitaxy and the role of the InAs/Al interface in hybrid two-dimensional electron gas systems

Control over epitaxy and the role of the InAs/Al interface in hybrid two-dimensional electron gas systems

Investigating the effects of impurity on electron mobility in quasi-one-dimensional wires

In this research, the electron mobility in GaAs quasi-one-dimensional wires with the presence of ionized impurity at zero temperatures was investigated and the results were compared with the mobility of a two-dimensional electron gas system. GaAs is a non-magnetic semiconductor with a direct band gap. Here for the calculations, the Boltzmann transport equation is used in the relaxation time approximation, taking into account the ionized impurity potential. Focusing on ionized Coulomb scattering and the short-range disorder is our goal. Electron mobility was investigated based on related parameters (Fermi energy and width of nanowires), and its diagram was drawn. In the end, the results of this research were compared with electron mobility in completely two-dimensional electronic systems. As expected, the numerical results showed that the electron mobility in extensive wires converges to the electron gas mobility of a fully two-dimensional plane.

Indium-bond-and-stop-etch (IBASE) technique for dual-side processing of thin high-mobility GaAs/AlGaAs epitaxial layers

We present a reliable flip-chip technique for dual-side processing of thin (<1 μm) high-mobility GaAs/AlGaAs epitaxial layers. The technique allows the fabrication of small (micron-scale with standard UV photolithography) patterned back gates and dual-gate structures on the thin GaAs/AlGaAs films with good alignment accuracy using only frontside alignment. The technique preserves the high-mobility (>106 cm2/V-s at 2 K) and most (>95%) of the charge density of the two-dimensional electron gas systems and allows linear control of the charge density with small (<1 V) electrostatic gate bias. Our technique is motivated by a THz quantum well detector based on intersubband transitions in a single, wide GaAs/AlGaAs quantum well, in which a symmetric, well-aligned dual-gate structure (with a typical gate dimension of ∼5 ×5 μm) is required for accurate and precise tuning of the THz detection frequency. Using our Indium-Bond-And-Stop-Etch technique, we realize such dual-gate structure on 660-nm thick GaAs/AlGaAs epitaxial layers that contain a modulation-doped, 40-nm wide, single square quantum well. By independently controlling the charge density and the DC electric field set between the gates, we demonstrate robust tuning of the intersubband absorption behavior of the 40-nm quantum well near 3.44 THz at 30 K.

Spatial distribution of photo-induced anomalous Hall effects of the top and bottom surface states in topological insulators Sb2Te3

Three-dimensional (3D) topological insulators (TIs) have attracted much attention due to their topologically protected surface states. Here, we use circularly polarized light to induce the photo-induced anomalous Hall effect (PAHE) in 3D TIs Sb2Te3 thin films with different thicknesses of 5, 7, 12 and 20 quintuple layers (QLs) at room temperature. The dependence of PAHE current on the light spot locations of Sb2Te3 thin films is investigated, which is found to show a completely different behavior from that observed in two-dimensional electron gas (2DEG) systems. This is due to the fact that the total PAHE current is the superposition of the PAHE of the top and bottom surface states. A theoretical model has been proposed to separate the PAHE current of the top and bottom surface states. In addition, as the thickness of the Sb2Te3 film increases from 5 QL to 20 QL, the PAHE currents of the top and bottom surface states first increase and then decrease. The photo-induced anomalous Hall, conductivity of the top surface states in the 7-QL Sb2Te3 film excited by 1064 nm light is as large as 592 nA⋅ V−1⋅ cm ⋅ W−1, which is much larger than that observed in InGaAs/AlGaAs quantum wells (4.45 nA⋅ V−1⋅ cm ⋅ W−1) and GaN/AlGaN heterostructures (1.43 nA⋅ V−1⋅ cm ⋅ W−1). The giant PAHE value observed in Sb2Te3 films suggests that 3D TIs may provide a good platform for spintronic devices.

Enhanced quantum oscillations and scattering effect in quaternary InAlGaN/GaN two-dimensional electron gas

Quantum transport properties of a large bandgap In0.15Al0.79Ga0.06N/GaN quaternary GaN high electron mobility transistor (HEMT) heterostructure are studied at low temperatures up to 2 K. Herein, we report the first evidence of weak localization in a quaternary GaN two-dimensional electron gas (2DEG) system. We observe negative magnetoresistance behavior and extracted dephasing time (τΦ) using a Hikami–Larkin–Nagaoka model at 2.2 K. Linear dependency of dephasing rate with temperature (τΦ−1∝T) is established below 20 K. Furthermore, Shubnikov–de Haas quantum oscillation induced by 2DEG is observed using perpendicular magnetic (B⊥) field strengths up to 14 T. From the temperature-dependent oscillation amplitude, we extracted an effective mass m*≈0.237me. The dominance of small-angle scattering in the 2DEG channel is identified from less than unit ratio (τq/τt≪1) of quantum lifetime (τq) to the Hall transport lifetime (τt). In our study, we have demonstrated that the In0.15Al0.79Ga0.06N/GaN quaternary heterostructure possesses high dephasing time (τΦ=5.4 ps) and larger quantum lifetime (τq=0.102 ps) indicating better suitability and a way forward to high-power–high-frequency GaN HEMT development.

Band structure of a nonparabolic two-dimensional electron gas system

Using angle-resolved photoelectron spectroscopy (ARPES), we study the band structures of two-dimensional electron gases (2DEGs) formed at Te-doped surfaces of InAs(110), as a result of band bending. The selected surface system is very clean and stable; therefore, ARPES spectra may be registered in short times, with minimal adsorption of residual gases and no photon beam-induced damage. We record a set of data that allows for a detailed analysis of the 2DEG band shapes, their thermal dependencies, and for an assessment of the many-body interactions. We find the electron-phonon interaction extremally weak and the electron-electron interactions hidden in dominant electron-donor interactions. While 2DEG band shapes are observed to be variable in correlation with the 2DEG density, this is tracked down to the variability of the band-bending potential and nonparabolicity of the system, and not to the many-body interactions. Thus, many-body renormalization of the 2DEG bands is not required, and the bands are described well by using the one-electron theoretical frame.

Electronic density response of warm dense matter

Matter at extreme temperatures and pressures—commonly known as warm dense matter (WDM)—is ubiquitous throughout our Universe and occurs in astrophysical objects such as giant planet interiors and brown dwarfs. Moreover, WDM is very important for technological applications such as inertial confinement fusion and is realized in the laboratory using different techniques. A particularly important property for the understanding of WDM is given by its electronic density response to an external perturbation. Such response properties are probed in x-ray Thomson scattering (XRTS) experiments and are central for the theoretical description of WDM. In this work, we give an overview of a number of recent developments in this field. To this end, we summarize the relevant theoretical background, covering the regime of linear response theory and nonlinear effects, the fully dynamic response and its static, time-independent limit, and the connection between density response properties and imaginary-time correlation functions (ITCF). In addition, we introduce the most important numerical simulation techniques, including path-integral Monte Carlo simulations and different thermal density functional theory (DFT) approaches. From a practical perspective, we present a variety of simulation results for different density response properties, covering the archetypal model of the uniform electron gas and realistic WDM systems such as hydrogen. Moreover, we show how the concept of ITCFs can be used to infer the temperature from XRTS measurements of arbitrary complex systems without the need for any models or approximations. Finally, we outline a strategy for future developments based on the close interplay between simulations and experiments.

Transport behaviors of topological band conduction in KTaO3’s two-dimensional electron gases

Two-dimensional electron gas systems (2DEGs) generated at the oxide interfaces that exhibit rich physics phenomena opened up an era for oxide-based electronics, photonics, and spintronics. The recent discovery of superconductivity plus the strong spin-orbital coupling naturally existing in the 2DEGs of KTaO3 (KTO) made KTO an exciting platform for the interplay of the electronic and spin degrees of freedom to create exotic physical properties. By directly placing KTO’s 2DEGs next to another strongly-correlated oxide with nontrivial topological nodes, we reveal the anomalous effects which were induced by the topological states in the electronic transport properties of the KTO’s 2DGEs, due to the electronic reconstruction caused by the proximity effect. This adds an additional prospect to the functions of KTO heterostructures.

Engineered Kondo screening and nonzero Berry phase in SrTiO3/LaTiO3/SrTiO3 heterostructures

Controlling the interplay between localized spins and itinerant electrons at the oxide interfaces can lead to exotic magnetic states. Here we devise SrTiO3/LaTiO3/SrTiO3 heterostructures with varied thickness of the LaTiO3 layer (n monolayers) to investigate the magnetic interactions in the two-dimensional electron gas system. The heterostructures exhibit significant Kondo effect when the LaTiO3 layer is rather thin (n = 2, 10), manifesting the strong interaction between the itinerant electrons and the localized magnetic moments at the interfaces, while the Kondo effect is greatly inhibited when n = 20. Notably, distinct Shubnikov-de Haas oscillations are observed and a nonzero Berry phase of {\pi} is extracted when the LaTiO3 layer is rather thin (n = 2, 10), which is absent in the heterostructure with thicker LaTiO3 layer (n = 20). The observed phenomena are consistently interpreted as a result of sub-band splitting and symmetry breaking due to the interplay between the interfacial Rashba spin-orbit coupling and the magnetic orderings in the heterostructures. Our findings provide a route for exploring and manipulating nontrivial electronic band structures at complex oxide interfaces.

Instability analysis of spin-electron-acoustic waves and the appearance of separated spin electron cyclotron mode in spin-polarized magnetized quantum plasma

Linear and nonlinear characteristics of electrostatic waves are studied in a magnetized plasma consisting of spin-up (n_{↑}) and spin-down (n_{↓}) state populations with uniformly distributed static ions in the background. The linear analysis shows the existence of four modes. One of these modes, termed the separated spin electron cyclotron wave, is found to be due to the separated spin populations. The Zakharov-Kuznetsov equationis derived by the reductive perturbation technique. The instability growth rate γ is obtained from the same equation. It is observed that the magnetized spin quantum plasma admits rarefactive soliton with constant amplitude but increasing width with the increasing strength of the applied magnetic field. It has also been observed that the amplitude of soliton decreases and its width increases with the increasing values of polarization ratio κ. The unstable region expands with the increase in polarization ratio and contracts with the increased plasma number density and magnetic-field strength. The (growth rate) γ of instability reduces by increasing the κ and is increasing when the density of the plasma and the strength of the magnetic field increasing. The model developed in this work finds its scope in studying degenerate electron gas and astrophysical systems such as pulsar magnetosphere and neutron stars.

The general analytical expression for computation of generalized relativistic Fermi-Dirac functions

In this paper, general sufficiently analytical formulae are developed for the arbitrary order generalized relativistic Fermi-Dirac (FD) functions. Analytical assessment of relativistic FD function is very important for various fields of physics especially in the theory of relativistic nondegenerate and degenerate electron gas systems. One of the more appropriate and correct approximations is based on a binomial expansion method and incomplete Gamma functions that have been used in the calculations of the generalized relativistic FD functions. Note that, the established expression in special cases of specific values of parameters becomes the evaluation formulae of other type FD functions. Calculation results of the generalized relativistic FD functions are compared with the other approximations methods and available numerical approaches and demonstrated satisfactory agreement.

Scattering-induced positive unsaturated linear magnetoresistance in LaAlO3/SrTiO3 two-dimensional electron gas system

In this paper, positive and unsaturated linear magnetoresistance (LMR) in an LaAlO3/SrTiO3 two-dimensional electron gas system is reported. LMR appears in this system over a wide range of temperatures and magnetic fields and does not tend to saturate at magnetic field up to 14 T. The spatial fluctuation in mobility is the most likely origin of positive unsaturated LMR because the existence of strong Shubnikov-de Haas oscillations rules out the extreme quantum origin. Moreover, LMR ∝ μ and HC ∝ 1/μ are confirmed and meet the requirements of Δμ/μ < 1 in the classical model proposed by Parish and Littlewood. This suggests that the observed LMR is the classical LMR effect induced by a narrow mobility distribution. These findings are of great interest for the practical application of magnetoresistive devices such as magnetic sensors, magnetometers, and magnetic storage devices.