Teslatronpt

The 1L-MoS₂ (or few-layer MoS₂) and SiP₂ flakes for electronic transport measurements were exfoliated onto a PDMS stamp and transferred onto a silicon substrate with prepatterned electrodes (Ti/Au with a thickness of 3/9 nm) in sequence. A top gate on the SiP₂ flake (Ti/Au with a thickness of 5/45 nm) was then made using electron-beam lithography and electron-beam evaporation. Electrical transport measurements were performed in a cryo-free superconducting magnet system (Oxford Instruments Teslatron^PT). Four-terminal resistance $R_{xx}$ was acquired using a Keithley 2182 voltmeter with a DC current supplied by a Keithley 2400 sourcemeter. The gate voltage is supplied by a Keithley 2400 sourcemeter. The sheet carrier density ( $n_{2\mathrm{D}}$ ) is obtained based on Hall effect measurements on Au/SiP₂/MoS₂ sandwiched devices^{22 (link)}. The Au/SiP₂/MoS₂ device can be considered as a parallel plate capacitor, and the amount of charge per unit area can be written as: $e{n}_{2\mathrm{D}}=\frac{{\epsilon }_0{\epsilon }_{\mathrm{r}-\mathrm{Si}{\mathrm{P}}_2}}{t_{\mathrm{Si}{\mathrm{P}}_2}}{V}_{\mathrm{tg}-\mathrm{Si}{\mathrm{P}}_2}$ where $e$ is the electron charge, ${\epsilon }_0$ is the vacuum permittivity, $t_{\mathrm{Si}{\mathrm{P}}_2}$  = 20 nm is the thickness of SiP₂, and ${\epsilon }_{\mathrm{r}-\mathrm{Si}{\mathrm{P}}_2}$ is the relative dielectric constant of SiP₂ within the Au/SiP₂/MoS₂ sandwiched structure. The ${\epsilon }_{\mathrm{r}-\mathrm{Si}{\mathrm{P}}_2}$ is obtained by linear fitting of Eq. (3).

Magneto-infrared spectroscopy was performed at ECNU by the FTIR spectrometer (Bruker 80 V) and a 12 T closed-cycle superconducting magnet (Oxford Instruments TeslatronPT). The collimated MIR (NIR) beam from a globar (tungsten) light source was guided into the variable temperature insert (VTI) of the magnet and then focused on the (0 0 1) surface of the EuCd₂As₂ crystal by an on-axis parabolic mirror. The experiment configuration is identical to that in NHMFL. The reflected infrared beam was propagating out of the VTI with the guidance of a brass light pipe and collected by the liquid-nitrogen-cooled detector located near the magnet. MCT and InSb detectors are used for MIR and NIR spectra, respectively.

The TiSe₂ crystals are mechanically exfoliated by scotch tape in a glove box with low concentration of H₂O and O₂ (<0.1 p.p.m.) and dry transferred onto the solid ion conductor substrates with pre-patterned electrodes (AlO_x/Ti/Au: 10/5/30 nm). The AlO_x layer prevents lithium ions from intercalating into the metal electrodes. The devices are then wire-bonded and loaded into a closed-cycle system (Oxford Instruments TeslatronPT) with a ³He insert. We install room temperature π filters (two 35 nF capacitors and one 220 μH inductor) to reduce the high-frequency noises. The resistance and Hall measurements are performed with the standard lock-in technique. The excitation current is chosen to be 1 μA (13 Hz), to avoid current-induced heating (Supplementary Fig. 9). The back-gate voltage is applied with a DC source-meter (Keithley 2400).