Mapping spin–charge conversion to the band structure in a topological oxide two-dimensional electron gas

Dyrdał

et al. 2020

Phys. Rev. Materials

Self Cite

Two-dimensional (2D) Rashba systems have been intensively studied in the last decade due to their unconventional physics, tunability capabilities, and potential for spin-charge interconversion when compared to conventional heavy metals. With the advent of a new generation of spin-based logic and memory devices, the search for Rashba systems with more robust and larger conversion efficiencies is expanding. Conventionally, demanding techniques such as angle-and spin-resolved photoemission spectroscopy are required to determine the Rashba parameter αR that characterizes these systems. Here, we introduce a simple method that allows a quantitative extraction of αR, through the analysis of the bilinear response of angle-dependent magnetotransport experiments. This method is based on the modulation of the Rashba-split bands under a rotating in-plane magnetic field. We show that our method is able to correctly yield the value of αR for a wide range of Fermi energies in the 2D electron gas at the LaAlO3/SrTiO3 interface. By applying a gate voltage, we observe a maximum αR in the region of the band structure where interband effects maximize the Rashba effect, consistently with theoretical predictions.

Section: Resultssupporting

confidence: 68%

“…Details of the tight-binding modelling can be found in Ref. [37]. We start by calculating α R = ∆k( 2 /2m * ) directly from the energy spectrum, where ∆k = k outer − k inner gives the difference of two neighbouring subbands.…”

Section: Resultsmentioning

confidence: 99%

Determining the Rashba parameter from the bilinear magnetoresistance response in a two-dimensional electron gas

Vaz

Dyrdał

et al. 2020

Phys. Rev. Materials

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“…In summary, we have demonstrated the realization of a 2DEG based on ferroelectric Ca:STO, with gate-tunable transport properties and different resistance states at remanence. Our results bring a new degree of freedom to functionalize further STO 2DEGs and control the spin-charge interconversion properties 12,44 and the superconducting response 22,45 by ferroelectricity. Future studies may aim at calculating and characterizing the electronic structure of such ferroelectric 2DEGs, explore the role of Casubstitution on the 2DEG properties, and possibly seek for room-temperature ferroelectricity, e.g.…”

mentioning

confidence: 90%

“…For the last 15 years, STO has also served as a platform to generate oxide two-dimensional electron gases (2DEGs) through the epitaxial growth of a polar perovskite such as LaAlO3 (LAO) 10 , the deposition of thin reactive metal films (such as Al) 11,12 or by fracturing in vacuum 13 . Although the precise mechanisms remain debated 14 , the formation of this n-type 2DEG often involves oxygen vacancies and is reminiscent of the ease by which bulk STO can be doped n-type.…”

Section: Introductionmentioning

confidence: 99%

Switchable two-dimensional electron gas based on ferroelectric Ca: SrTiO3

Bréhin

Vicente-Arche

et al. 2020

Phys. Rev. Materials

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Two-dimensional electron gases (2DEGs) can form at the surface of oxides and semiconductors or in carefully designed quantum wells and interfaces. Depending on the shape of the confining potential, 2DEGs may experience a finite electric field, which gives rise to relativistic effects such as the Rashba spinorbit coupling. Although the amplitude of this electric field can be modulated by an external gate voltage, which in turn tunes the 2DEG carrier density, sheet resistance and other related properties, this modulation is volatile. Here, we report the design of a "ferroelectric" 2DEG whose transport properties can be electrostatically switched in a non-volatile way. We generate a 2DEG by depositing a thin Al layer onto a SrTiO3 single crystal in which 1% of Sr is substituted by Ca to make it ferroelectric. Signatures of the ferroelectric phase transition at 25 K are visible in the Raman response and in the temperature dependences of the carrier density and sheet resistance that shows a hysteretic dependence on electric field as a consequence of ferroelectricity. We suggest that this behavior may be extended to other oxide 2DEGs, leading to novel types of ferromagnet-free spintronic architectures.

“…It can also be the basis of logic devices 22 akin to the magnetoelectric spin-orbit (MESO) device proposed by Intel 23 , but without resorting to a multiferroic to switch the ferromagnet. To experimentally demonstrate the non-volatile electrical control of the spin-charge conversion, we use SrTiO3 (STO) 2DEGs, generated by the deposition of a film of Al onto a STO single crystal 24,25 . Indeed, STO 2DEGs exhibit a sizeable Rashba SOC 10 with a very high conversion efficiency 25,26 .…”

mentioning

confidence: 99%

Non-volatile electric control of spin–charge conversion in a SrTiO3 Rashba system

Noël

Vicente-Arche

et al. 2020

Nature

Self Cite

192

136

After 50 years of exponential increase in computing efficiency, the technology of today's electronics is approaching its physical limits, with feature sizes smaller than 10 nm. New schemes must be devised to contain the ever-increasing power consumption of information and communication systems 1 , which requires the introduction of non-traditional materials and new state variables. As recently highlighted 2 , the remanence associated with collective switching in ferroic systems is appealing to reduce power consumption. A particularly promising approach is spintronics, which relies on ferromagnets to provide non-volatility and to generate and detect spin currents 3. However, magnetization reversal by spin transfer torques 4 is a power consuming process. This is driving research on multiferroics to achieve a low-power electricfield control of magnetization 5 , but practical materials are scarce and magnetoelectric switching remains difficult to control. Here, we demonstrate an alternative strategy to achieve low-power spin detection, in a non-magnetic system. We harness the electric-field-induced ferroelectriclike state of SrTiO3 6-9 to manipulate the spin-orbit properties 10 of a two-dimensional electron gas 11 , and efficiently convert spin currents into positive or negative charge currents, depending on the polarisation direction. This non-volatile effect opens the way to the electric-field control of spin currents and to ultralow-power spintronics, in which non-volatility would be provided by ferroelectricity rather than by ferromagnetism.