Hard x-ray angle-resolved photoemission from a buried high-mobility electron system

Abstract

Novel two-dimensional electron systems at the interfaces and surfaces of transition-metal oxides recently have attracted much attention as they display tunable, intriguing properties that can be exploited in future electronic devices. Here we show that a high-mobility quasi-two-dimensional electron system with strong spin-orbit coupling can be induced at the surface of a KTaO 3 (001) crystal by pulsed laser deposition of a disordered LaAlO 3 film. The momentum-resolved electronic structure of the buried electron system is mapped out by hard x-ray angle-resolved photoelectron spectroscopy. From a comparison to calculations, it is found that the band structure deviates from that of electron-doped bulk KTaO 3 due to the confinement to the interface. Fermi surface mapping shows a three-dimensional, periodic intensity pattern consistent with electron pockets of quantum well states centered around the points and the expectations from a Fourier analysis-based description of photoemission on confined electron systems. From the k broadening of the Fermi surface and core-level depth profiling, we estimate the extension of the electron system to be at least 1 nm but not much larger than 2 nm, respectively.

Orientation-dependent electron-phonon coupling in interfacial superconductors LaAlO3/KTaO3

“…So far its superconducting paring mechanism remains debated [3][4][5][6][7][8][9][10][11][12][13]. Recently, a second family of oxide interfacial superconductors is discovered at LaAlO 3 /KTaO 3 (LAO/KTO) and EuO/KTaO 3 , which soon becomes a new research spotlight [14][15][16][17][18][19][20][21]. Remarkably, the superconductivity develops at T c ∼ 2 K at LAO/KTO(111) [14,15], T c ∼ 0.9 K at LAO/KTO(110) [19], but is absent at LAO/KTO(001) down to 25 mK [14].…”

“…It is still challenging for angle-resolved photoemission spectroscopy (ARPES) measurements due to its surface sensitivity. Though the bulk-sensitive hard X-ray ARPES could reach the buried interfacial states [18], it lacks the energy/momentum resolution for clearly revealing the dispersive information. Here we overcome this difficulty by studying superconducting interfaces with the thinnest overlayers and exploiting ∼1000 eVphoton-excited soft X-ray (SX-) ARPES with adequate probing depth and decent energy/momentum resolution [30,31].…”

Evidence of linear and cubic Rashba effect in non-magnetic heterostructure

“…Due to the comparable band gaps and lattice parameters, LaAlO 3 and KTaO 3 are considered as very good candidates for creating heterostructure with an effective charge accumulation at the interfaces. Recently, there have been theoretical and experimental studies of LaAlO 3 /KTaO 3 heterostructures [37,38]. However, a detailed first-principle study on the effect of intrinsic SOC and the possibility of RSO interaction has remained unexplored.…”