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The formation of a two-dimensional electron gas (2DEG) at the interface between two insulators SrTiO 3 (STO) and
LaAlO 3 (LAO) is among the most intriguing finding in oxide electronics. In recent years, several exotic phenomena
including superconductivity [1], Rashba spin-orbit coupling [2], ferromagnetism and quantum oscillations [3] have
been reported at this interface. While the theoretical calculations for band structure reveal the formation of
several subbands (d xy , d xz and d yz ) arising from the interface crystal field splitting of Ti:3d t 2g orbital, no clear
consensus has been reached yet from experimental evidences. Here, I investigate the quantum transport of a high
mobility 2DEG at LAO/STO interface under high magnetic field (55T). Surprisingly, the Shubnikov-de Haas
oscillations (SdHO) of the longitudinal resistance (R xx ) are aperiodic when plotted as a function of inverse magnetic
field. This observation, at the origin of a non-linear Landau fan diagram, contrasts with a linear Hall resistance (R xy )
over the full magnetic field range. In this seminar, I will explore different scenarios to explain the peculiar transport
properties of such 2DEG at LAO/STO interface. In particular, I will show that the Roth-Gao-Niu model [4], where
the phase of the magnetic oscillations depends both on energy and magnetic field, provides a natural explanation
of the experimental results.
Fig. Magnetic field dependence of the longitudinal resistance (R xx ) in LAO/STO 2DEG for different back-gate
voltages. The dot lines are guides for the eye. The inset shows an optical microscopy image of LAO/STO device.
References
[1] A. Joshua et al., Nature Comm. 3, 1129 (2012); J. Biscaras et al., Phys. Rev. Lett. 108, 247004 (2012).
[2] A. D. Caviglia et al., Phys. Rev. Lett. 104, 126803 (2010); Z. Zhong et al., Phys. Rev. B 87, 161102(R) (2013).
[3] B. Shalom et al., Phys. Rev. Lett. 105, 206401 (2010); M. Yang et al., App. Phys. Lett. 109, 122106 (2016).
[4] Y. Gao and Q. Niu, PNAS 114, 7295 (2017) ; J.N. Fuchs et al., SciPost Phys. 4, 024 (2018) |