Recent News

Electron pairing and nematicity in LaAlO3/SrTiO3 nanostructures

Strongly correlated electronic systems exhibit a wealth of unconventional behavior stemming from strong electron-electron interactions. The LaAlO3/SrTiO3 (LAO/STO) heterostructure supports rich and varied low-temperature transport characteristics including low-density superconductivity, and electron pairing without superconductivity for which the microscopic origins is still not understood. LAO/STO also exhibits inexplicable signatures of electronic nematicity via nonlinear and anomalous Hall effects. Nanoscale control over the conductivity of the LAO/STO interface enables mesoscopic experiments that can probe these effects and address their microscopic origins. Here we report a direct correlation between electron pairing without superconductivity, anomalous Hall effect and electronic nematicity in quasi-1D ballistic nanoscale LAO/STO Hall crosses. The characteristic magnetic field at which the Hall coefficient changes directly coincides with the depairing of non-superconducting pairs showing a strong correlation between the two distinct phenomena. Angle-dependent Hall measurements further reveal an onset of electronic nematicity that again coincides with the electron pairing transition, unveiling a rotational symmetry breaking due to the transition from paired to unpaired phases at the interface. The results presented here highlights the influence of preformed electron pairs on the transport properties of LAO/STO and provide evidence of the elusive pairing “glue” that gives rise to electron pairing in SrTiO3-based systems. 

Surface acoustic wave generation and detection in the quantum paraelectric regime of SrTiO3-based heterostructures 

Strontium titanate (STO), apart from being a ubiquitous substrate for complex-oxide heterostructures, possesses a multitude of strongly coupled electronic and mechanical properties. Surface acoustic wave (SAW) generation and detection offers insight into electromechanical couplings that are sensitive to quantum paraelectricity and other structural phase transitions. Propagating SAWs can interact with STO-based electronic nanostructures, in particular LaAlO3/SrTiO3 (LAO/STO). Here, we report the generation and detection of SAW within LAO/STO heterointerfaces at cryogenic temperatures (T 2 K) using superconducting interdigitated transducers. The temperature dependence shows an increase in the SAW quality factor that saturates at T ≈ 8 K. The effect of backgate tuning on the SAW resonance frequency shows the possible acoustic coupling with the ferroelastic domain wall evolution. This method of generating SAWs provides a pathway towards the dynamic tuning of ferroelastic domain structures, which are expected to influence the electronic properties of complex-oxide nanostructures. Devices that incorporate SAWs may in turn help to elucidate the role of ferroelastic domain structures in mediating electronic behavior. 

Mott-Limited Thermopower of Pascal Electron Liquid Phases at the LaAlO3/SrTiO3 Interface 

The thermoelectric properties of quasi-1D electron waveguides at the LaAlO3/ SrTiO3 interface at millikelvin temperatures are investigated. A highly enhanced and oscillating thermopower is found for these electron waveguides, with values exceeding 100 μV K1 at 0.1 K in the electron-depletion regime. The Mott relation, which governs the band-term thermopower of noninteracting electrons, agrees well with the experimental findings in and around regimes where strongly attractive electron–electron interactions lead to a previously reported Pascal series of conductance explained by bound states of n ¼ 2, 3, 4, ... electrons. These results pave the way for quantized thermal transport studies of emergent electron liquid phases in which transport is governed by quasiparticles with charges that are integer multiples or fractions of an electron.

Preparing Precollege Students for the Second Quantum Revolution with Core Concepts in Quantum Information Science 

After the passage of the U.S. National Quantum Initiative Act in December 2018,1 the National Science Foundation (NSF) and the Office of Science and Technology Policy (OSTP) recently assembled an interagency working group and conducted a workshop titled “Key Concepts for Future Quantum Information Science Learners” that focused on identifying core concepts for future curricular and educator activities2,3 to help precollege students engage with quantum information science (QIS). Helping precollege students learn these key concepts in QIS is an effective approach to introducing them to the second quantum revolution and inspiring them to become future contributors in the growing field of quantum information science and technology as leaders in areas related to quantum computing, communication, and sensing. This paper is a call to precollege educators to contemplate including QIS concepts into their existing courses at appropriate levels and get involved in the development of curricular materials suitable for their students. Also, research shows that compare-and-contrast activities can provide an effective approach to helping students learn.4 Therefore, we illustrate a pedagogical approach that contrasts the classical and quantum concepts so that educators can adapt them for their students in their lesson plans to help them learn the differences between key concepts in quantum and classical contexts.