Design and performance of an ultra-high vacuum spin-polarized scanning tunneling microscope operating at 30 mK and in a vector magnetic field

Abstract

We describe the design and performance of a scanning tunneling microscope (STM) that operates at a base temperature of 30 mK in a vector magnetic field. The cryogenics is based on an ultra-high vacuum (UHV) top-loading wet dilution refrigerator that contains a vector magnet allowing for fields up to 9 T perpendicular and 4 T parallel to the sample. The STM is placed in a multi-chamber UHV system, which allows in situ preparation and exchange of samples and tips. The entire system rests on a 150-ton concrete block suspended by pneumatic isolators, which is housed in an acoustically isolated and electromagnetically shielded laboratory optimized for extremely low noise scanning probe measurements. We demonstrate the overall performance by illustrating atomic resolution and quasiparticle interference imaging and detail the vibrational noise of both the laboratory and microscope. We also determine the electron temperature via measurement of the superconducting gap of Re(0001) and illustrate magnetic field-dependent measurements of the spin excitations of individual Fe atoms on Pt(111). Finally, we demonstrate spin resolution by imaging the magnetic structure of the Fe double layer on W(110).

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

“…More recently, fueled by further interest in increased energy resolution to probe the low temperature quantum phases of matter, [8][9][10] STM systems have been built based on a dilution refrigerator design (DR), which have achieved mK operational temperatures. [11][12][13][14][15][16][17][18] Complementary to traditional STS, spin-resolved STM/STS methods have been used to study the magnetic properties of individual atoms. 7,19,20 Nevertheless, spin-resolved STM/STS typically measures time-averaged properties due to the poor time resolution 21,22 that is limited by the bandwidth of the transimpedance preamplifier.…”

“…Here, based on a recent ultra-high vacuum (UHV) spinresolved DR-STM operational at mK temperatures and in a vector magnetic field, 18,37 we detail the implementation and performance of both ESR and pump-probe methods at mK temperatures in this system. We demonstrate the ESR-STM operation in two different modes, namely, the frequency sweep ( f -sweep) and magnetic field sweep (B-sweep) mode.…”

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

“…5 A steady increase in sophistication in SPM instruments has occurred roughly over the four decades since the introduction of the technique, with a resurgence of instrumentation development into ultra-low temperature environments beginning in the early 2000s and increasing steadily since then. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Although SPM instruments have been developed that operate at temperatures down to ≈ 10 mK, none of them have achieved a tunneling energy resolution equivalent to their operating temperature. More typically, instruments show a noise-induced operating resolution equivalent to 150 mK-200 mK, 10,12,17,20,21 even though the instrument is operating at temperatures of almost ten times lower, although some progress has been made recently demonstrating tunneling resolutions below 100 mK.…”

“…[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Although SPM instruments have been developed that operate at temperatures down to ≈ 10 mK, none of them have achieved a tunneling energy resolution equivalent to their operating temperature. More typically, instruments show a noise-induced operating resolution equivalent to 150 mK-200 mK, 10,12,17,20,21 even though the instrument is operating at temperatures of almost ten times lower, although some progress has been made recently demonstrating tunneling resolutions below 100 mK. 13,19 In contrast, magnetotransport instruments deliver measurements with resolutions close to their base temperatures of (10 mK-20 mK).…”

Upgrade of a low-temperature scanning tunneling microscope for electron-spin resonance

“…The spectroscopic energy resolution of an STM is limited by the Fermi-Dirac distributions of tip and sample. This stimulated the development of dedicated low-temperature SPMs, operating well below the boiling point of liquid helium [1][2][3][4][5].…”