A sub-2 Kelvin cryogenic magneto-terahertz scattering-type scanning near-field optical microscope (cm-THz-sSNOM)

Abstract

We have developed a versatile near-field microscopy platform that can operate at high magnetic fields and below liquid-helium temperatures. We use this platform to demonstrate an extreme terahertz (THz) nanoscope operation and to obtain the first cryogenic magneto-THz time-domain nano-spectroscopy/imaging at temperatures as low as 1.8 K, magnetic fields of up to 5 T, and with operation of 0–2 THz. Our Cryogenic Magneto-Terahertz Scattering-type Scanning Near-field Optical Microscope (or cm-THz-sSNOM) instrument is comprised of three main equipment: (i) a 5 T split pair magnetic cryostat with a custom made insert, (ii) a custom sSNOM instrument capable of accepting ultrafast THz excitation, and (iii) a MHz repetition rate, femtosecond laser amplifier for broadband THz pulse generation and sensitive detection. We apply the cm-THz-sSNOM to obtain proof of principle measurements of superconductors and topological semimetals. The new capabilities demonstrated break grounds for studying quantum materials that require an extreme environment of cryogenic operation and/or applied magnetic fields in nanometer space, femtosecond time, and THz energy scales.

Hyperbolic exciton polaritons in a van der Waals magnet

“…Improving quality may also enable imaging of the surface mode – observations of surface exciton polaritons are rare 49 , 50 and near-field imaging could provide direct proof of their existence. Finally, measuring CrSBr in an s-SNOM capable of applying magnetic fields 51 , 52 would allow for studying the interplay between HEP propagation and magnetic order.…”

Ultrabroadband Terahertz Near-Field Nanospectroscopy with a HgCdTe Detector

“…While here we demonstrate synchrotron-based THz nanospectroscopy, we emphasize that our detector system is expected to work equally well for laser-based THz nanoimaging and nanospectroscopy setups, e.g., based on free-electron-lasers, ,,,− gas lasers, ,, or THz quantum cascade lasers. ,, The high signal-to-noise ratio of our measurements implies that our technique will also provide great opportunities for studying the THz polariton dispersion in other van der Waals and two-dimensional materials, e.g., in graphene, , black phosphorus, transition metal dichalcogenides, or topological insulators such as Bi 2 Se 3 . ,, Furthermore, access to a plethora of new phenomena is expected when combining the here presented ultrabroadband THz nanospectroscopy with extreme sample environments in cryogenic ,− or magnetic , near-field microscopy. For example, this may enable the nanoscopic exploration of Cooper-pair and Josephson plasmon polaritons in superconductors that exclusively reside in the THz range. ,, Overall, our work demonstrates the extension of broadband infrared near-field nanospectroscopy well into the single-digit THz range, thereby significantly extending the possibilities for nanoscale optical material characterization and probing fundamental collective excitations at their natural length and energy scales.…”

“…32,37,38 The high signal-to-noise ratio of our measurements implies that our technique will also provide great opportunities for studying the THz polariton dispersion in other van der Waals and two-dimensional materials, e.g., in graphene, 28,36 black phosphorus, 6 transition metal dichalcogenides, 29 or topological insulators such as Bi 2 Se 3 . 6,32,33 Furthermore, access to a plethora of new phenomena is expected when combining the here presented ultrabroadband THz nanospectroscopy with extreme sample environments in cryogenic 29,63−68 or magnetic 69,70 nearfield microscopy. For example, this may enable the nanoscopic exploration of Cooper-pair and Josephson plasmon polaritons in superconductors that exclusively reside in the THz range.…”

Hyperbolic exciton polaritons in a van der Waals magnet

“…Improving quality may also enable imaging of the n = 0 surface mode -observations of surface exciton polaritons are rare (48-49) and near-eld imaging could provide direct proof of their existence. Finally, measuring CrSBr in an s-SNOM capable of applying magnetic elds (50)(51) would allow for studying the interplay between HEP propagation and magnetic order. Competing interests: The authors declare no competing nancial interests.…”