Achieving μeV tunneling resolution in an in-operando scanning tunneling microscopy, atomic force microscopy, and magnetotransport system for quantum materials research

Abstract

Research in new quantum materials requires multi-mode measurements spanning length scales, correlations of atomic-scale variables with a macroscopic function, and spectroscopic energy resolution obtainable only at millikelvin temperatures, typically in a dilution refrigerator. In this article, we describe a multi-mode instrument achieving a μeV tunneling resolution with in-operando measurement capabilities of scanning tunneling microscopy, atomic force microscopy, and magnetotransport inside a dilution refrigerator operating at 10 mK. We describe the system in detail including a new scanning probe microscope module design and sample and tip transport systems, along with wiring, radio-frequency filtering, and electronics. Extensive benchmarking measurements were performed using superconductor-insulatorsuperconductor tunnel junctions, with Josephson tunneling as a noise metering detector. After extensive testing and optimization, we have achieved less than 8 μeV instrument resolving capability for tunneling spectroscopy, which is 5-10 times better than previous instrument reports and comparable to the quantum and thermal limits set by the operating temperature at 10 mK.

Edge channels of broken-symmetry quantum Hall states in graphene visualized by atomic force microscopy

“…Measurements of macroscopic and microscopic quantum Hall properties were made using an instrument that is capable of simultaneous magnetotransport, scanning tunneling microscopy, and AFM measurements on a given device at ultralow temperatures 37 , 38 . The instrument was operated at 10 mK for all measurements with a perpendicular magnetic field up to 15 T. Magnetotransport measurements of the Hall and longitudinal resistances are shown in Fig.…”

“…Using the probe tip reflection, a tip-sample gap of the order of 100 µm is set at room temperature. The module is then transferred and locked into the dilution refrigerator multimode SPM system where it is cooled to a temperature of 10 mK 37 , 38 . The landing region is scanned, and a ridge is identified after approaching the fan-shaped runway surface.…”

“…Magnetotransport measurements were performed using a lock-in amplifier at 25 Hz with a 10 nA source current. The qPlus AFM sensor was a new design that incorporated an integrated excitation electrode on the sensor 38 . The qPlus sensor had a quality factor of and a resonance frequency of f 0 = 23.4 kHz at zero magnetic field.…”

A scanning tunneling microscope capable of electron spin resonance and pump–probe spectroscopy at mK temperature and in vector magnetic field

“…1, we utilized the Josephson peak of a superconductor-insulator-superconductor (SIS) junction as a noise sensor. [40][41][42] We prepared a Re(0001) sample by initial cycles of Ar + sputtering, followed by subsequent cycles of O 2 annealing (T ∼ 1500 K) and flash annealing (T ≙ 1830 K). Then, we picked up a Re cluster on a W tip to obtain an asymmetric SIS junction of 2(Δ 1 + Δ 2 ) ≈ 2.23 mV [Fig.…”

Field-Tunable One-Sided Higher-Order Topological Hinge States in Dirac Semimetals

“…We numerically check the robustness of the one-sided hinge states against weak disorder, and expect the one-sided hinge states to be detectable in the state-of-the-art scanning tunneling Hall measurement (Fig. 4) [77]. This work will not only help identify the Fermi-arc 3D quantum Hall effect but also be insightful for searching for higher-order topological states of matter.…”