Phys.org September 22, 2024 Non-centrosymmetric polar conductors are intrinsic diodes that could be of use in the development of nonlinear applications. Such systems have recently been extended to non-centrosymmetric superconductors. An international team of researchers (USA – Harvard University, Northeastern University, MIT, UCLA, Boston College, Taiwan, India, Japan) has reported antiferromagnetic diode effect in a centrosymmetric crystal without directional charge separation. Large second-harmonic transport in a nonlinear electronic device enabled by the compensated antiferromagnetic state of even-layered MnBi2Te4. They showed that this antiferromagnetic diode effect could be used to create in-plane field-effect transistors and microwave-energy-harvesting devices, and electrical sum-frequency generation […]
Tag Archives: Quantum materials
A new approach to fine-tuning quantum materials
MIT News August 12, 2024 For topological Weyl semimetals, there is a pressing need to fine-tune the Fermi level, a critical aspect of quantum materials, to the Weyl nodes and unlock exotic electronic and optoelectronic effects associated with the divergent Berry curvature. However, the situation for bulk crystals poses significant challenges. A team of researchers in the US (MIT, Brookhaven National Laboratory, industry) demonstrated the meV level ultra-fine-tuning of the Fermi level of bulk topological Weyl semimetal tantalum phosphide. By calculating the desired carrier density and controlling the accelerator profiles, the Fermi level could be experimentally fine-tuned from 5 meV below, […]
An MRI-like tool for quantum materials: Sensor can detect minute magnetic fields at atomic scale
Phys.org July 25, 2024 The detection of faint magnetic fields from single-electron and nuclear spins at the atomic scale is a long-standing challenge in physics. While current mobile quantum sensors achieve single-electron spin sensitivity, atomic spatial resolution remains elusive for existing techniques. An international team of researchers (Germany, South Korea) fabricated a single-molecule quantum sensor at the apex of the metallic tip of a scanning tunnelling microscope by attaching Fe atoms and a PTCDA (3,4,9,10-perylenetetracarboxylic-dianhydride) molecule to the tip apex. They addressed the molecular spin by electron spin resonance and achieved ~100 neV resolution in energy. In a proof-of-principle experiment, they […]
Physicists reach atomic-scale telegraphy with light
Phys.org May 8, 2024 By exploiting linear interaction with tip-confined evanescent light fields, near-field microscopy has reached even higher resolution, prompting a vibrant research field by exploring the nanocosm in motion. Yet the finite radius of the nanometre-sized tip apex has prevented access to atomic resolution. Researchers in Germany leveraged extreme atomic nonlinearities within tip-confined evanescent fields to push all-optical microscopy to picometric spatial and femtosecond temporal resolution. They discovered an unprecedented and efficient non-classical near-field response, in phase with the vector potential of light and strictly confined to atomic dimensions. This ultrafast signal was characterized by an optical phase […]
Quantum dance to the beat of a drum: Researchers observe how energy of single electron is tuned by surrounding atoms
Phys.org March 14, 2024 Direct observation of the relevant interplay of the electronic structure of a single defect with other microscopic elementary excitations on their intrinsic length, time and energy scales has not been achieved. Researchers in Germany directly resolved in space, time, and energy how a spin–orbit-split energy level of an isolated selenium vacancy in a moiré-distorted WSe2 monolayer evolved under the controlled excitation of lattice vibrations. By locally launching a phonon oscillation and taking ultrafast energy-resolved snapshots of the vacancy’s states faster than the vibration period, they directly measured the impact of electron–phonon coupling in an isolated single-atom […]
Materials research explores design rules and synthesis of quantum memory candidates
Phys.org March 11, 2024 Stoichiometric Eu3+ compounds have recently shown promise for building dense, optically addressable quantum memory as the cations’ long nuclear spin coherence times and shielded 4f electron optical transitions provide reliable memory platforms but finding rare linewidth behavior within a wide range of potential chemical spaces remains difficult. Researchers at the University of Illinois, Urbana─Champaign, have found density functional theory (DFT) procedures that reliably reproduce known phase diagrams and correctly predict two experimentally realized quantum memory candidates. They synthesized the double perovskite halide Cs2NaEuF6 which is an air-stable compound with a calculated band gap of 5.0 eV […]
Widely tunable terahertz lasers boost photo-induced superconductivity in K₃C₆₀
Phys.org October 12, 2023 Photoexcitation at terahertz and mid-infrared frequencies has emerged as an effective way to manipulate functionalities in quantum materials, in some cases creating non-equilibrium phases that have no equilibrium analogue. In K3C60, a metastable zero-resistance phase was observed that has optical properties, nonlinear electrical transport, and pressure dependencies compatible with non-equilibrium high-temperature superconductivity. An international team of researchers (Germany, Switzerland, Italy, UK) demonstrated a two-orders-of-magnitude increase in photo-susceptibility near 10 THz excitation frequency. At these drive frequencies, a metastable superconducting-like phase was observed up to room temperature. The discovery of a dominant frequency scale sheds light on the […]
Physicists coax superconductivity and more from quasicrystals
Phys.org September 28, 2023 Owing to their complexity and scarcity, quasicrystals are underexplored relative to periodic and amorphous structures. An international team of researchers (USA – MIT, Japan, Israel) introduced a new type of highly tunable quasicrystal easily assembled from periodic components. By twisting three layers of graphene with two different twist angles, they formed two mutually incommensurate moiré patterns. In contrast to many common atomic-scale quasicrystals, the quasiperiodicity in their system was defined on moiré length scales of several nanometres. This ‘moiré quasicrystal’ allowed them to tune the chemical potential and thus the electronic system between a periodic-like regime […]
Physicists discover first transformable nanoscale electronic devices
Phys.org April 17, 2023 Interfaces of van der Waals (vdW) materials, such as graphite and hexagonal boron nitride (hBN), exhibit low friction sliding due to their atomically flat surfaces and weak vdW bonding. An international team of researchers (UC Irvine, Japan) has demonstrated that microfabricated gold also slides with low friction on hBN. This enables the arbitrary post-fabrication repositioning of device features both at ambient conditions and in situ to a measurement cryostat. They demonstrated mechanically reconfigurable vdW devices where device geometry and position are continuously tunable parameters. By fabricating slidable top gates on a graphene-hBN device, they produced a […]
Breakthrough discovery in materials science challenges current understanding of photoemission
Phys.org March 14, 2023 Currently existing photocathodes are based on conventional metals and semiconductors that were discovered six decades ago with sound theoretical underpinnings. An international team of researchers (China, Japan, USA- Northeastern University) has observed unusual photoemission properties of a reconstructed surface of SrTiO3(100) single crystals. Unlike other positive-electron-affinity (PEA) photocathodes, their PEA SrTiO3 surface produced discrete secondary photoemission spectra at room temperature, characteristic of the efficient negative-electron-affinity photocathode materials. Using several photon energies they were able to produce a very intense coherent secondary photoemission. According to the researchers the observed emergence of coherence in secondary photoemission points to […]