Shubnikov–De Haas Oscillations inSrTiO3/LaAlO3Interface

Abstract

Quantum magnetic oscillations in SrTiO3/LaAlO3 interface are observed. The evolution of their frequency and amplitude at various gate voltages and temperatures is studied. The data are consistent with the Shubnikov de-Haas theory. The Hall resistivity ρxy exhibits nonlinearity at low magnetic field. ρxy is fitted assuming multiple carrier contributions. The comparison between the mobile carrier density inferred from the Hall data and the oscillation frequency suggests multiple valley and spin degeneracy. The small amplitude of the oscillations is discussed in the framework of the multiple band scenario. PACS numbers: 75.70.Cn, The two dimensional electron gas (2DEG) formed at the interface between two insulating perovskites is a subject of intense scientific interest.[1] The most widely studied interface has been the one created between SrTiO 3 and LaAlO 3 .[2] At low temperatures this 2DEG has a superconducting ground state, whose critical temperature can be modified by an electric field effect.[3]The nature of the charge carriers and their origin are still a matter of debate. [4][5][6][7][8][9][10][11] The thickness of the conducting layer has been estimated to be of a few nanometers by both transport measurements [12][13] and by using a conducting atomic force microscope (AFM). [14] From the AFM data analysis Copie et al. conclude that two types of charge carriers screen the local electric fields. The magnetoresistance is strongly anisotropic [12] and effected by a gate dependent spin-orbit interaction. [15,16] The ρ xy is non linear in magnetic field, [15,17] and therefore it does not relate in a simple way to the number of charge carriers. The effective mass has been estimated using elipsometry[18] to be 2.2 m e with m e the electron mass. The number of charge carriers, their effective mass and the effect of gate voltage on their mobility are a subject of vigorous research.Quantum oscillations in magnetic fields have been extensively used to study the electronic properties of metals semiconductors and correlated systems. In the standard theory of Shubnikov-de Haas (SdH) the amplitude of the oscillating part of the resistance is [19]Where R c is the non-oscillating part of the resistance. The oscillation amplitude decays with temperature as given bywith m * the quasiparticle effective mass. The Dingle factor iswith ω c = eB m * and τ D the Dingle scattering time, which is related to the Dingle temperature by k B T D = /2πτ D . This factor determines the decay of the amplitude of the oscillations as the field decreases. Increasing the magnetic field, lowering the temperatures and decreasing the scattering rate should all lead to increasing oscillations amplitude.In this letter we report longitudinal and Hall resistance measurements at low temperatures and intense magnetic fields of up to 31.5 T. The high magnetic field enables us to detect quantum oscillations in the longitudinal resistivity, as well as nonlinearities in the Hall resistance. The data are consistent with the SdH theory, enabling us to extract ...

Giant spin splitting of the two-dimensional electron gas at the surface of SrTiO3

“…This suggests that the mechanism responsible for the helical in-plane spin texture is the main energy scale at large momenta. This energy scale is then one order of magnitude larger than both the one so far reported in LaAlO 3 /SrTiO 3 interfaces [10,11], and the one expected from a naive Rashba model that takes solely into account the confining electric field. Such a strong deviation from the original Rashba scenario has been demonstrated for model metallic systems by numerous previous works [23,24], and is attributed as a general property of the surface corrugation and the associated wave-function asymmetry [23][24][25][26], which results in a greatly enhanced Rashba parameter that increases the spin splitting.…”

“…For F ∼ 100 MV/m and ∆ ∼ 3.5 eV, typical of the 2DEG at the surface of SrTiO 3 [12,15], the momentum spin splitting at E F is thus expected to be of the order of k R ∼ 6 × 10 −3Å−1 , at the limit of the best resolutions today available in ARPES. For the light subbands in SrTiO 3 , such momentum splitting amounts to an energy splitting of a few meV near E F , as indeed inferred from magnetotransport measurements in the 2DEG at LaAlO 3 /SrTiO 3 interfaces subject to a strong voltage bias [10,11], and also predicted by ab initio calculations of the 2DEG at such interfaces [16,17]. However, the possible spin splitting of the 2DEG at the surface of SrTiO 3 has not been measured so far.…”

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1 Two-dimensional electron gases (2DEGs) forming at the interfaces of transition metal oxides [1][2][3] display a range of properties including tunable insulatorsuperconductor-metal transitions [4][5][6], large magnetoresistance [7], coexisting ferromagnetism and superconductivity [8, 9], and a spin splitting of a few meV [10,11]. Strontium titanate (SrTiO 3 ), the cornerstone of such oxide-based electronics, is a transparent, nonmagnetic, wide-band-gap insulator in the bulk, and has recently been found to host a surface 2DEG [12][13][14][15].

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Insulator-to-Metal Transition at Oxide Interfaces Induced by WO3 Overlayers

“…Furthermore, the obtained n SdH is lower than both n II , n I for this sample, so that it is not possible to associate the SdH oscillation to one specific channel. A discrepancy between n SdH and n Hall in LAO/STO interfaces has already been reported and its origin remains unknown [33,34].…”

Tunable coupling of two-dimensional superconductors in bilayer SrTiO3heterostructures

“…Inter-sub-band scattering (a) quantized sub-bands [17,[22][23][24][25][26][27][28][29][30][31][32]. Thus a consistent understanding of both the normal and the superconducting states requires consideration of the sub-band structure in the electrostatic confinement potential which must be considered self-consistently throughout the system as a whole.…”