Browsing by Author "Chen, LiYang"

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    Nosie measurement in strongly correlated systems
    (2023-04-17) Chen, LiYang; Natelson, Douglas; Dai, Pengcheng; Zhu, Hanyu
    Noise comes from the current or voltage fluctuations in devices. The three most common types of noise are thermal noise, 1/f noise, and shot noise. Correctly interpreting noise signal can provide extra information beyond common electron transport experiments. In this thesis, we used the noise signal to study the strongly correlated materials, and found interesting results in two different systems, a Mott insulator and a strange metal. This thesis starts from introduction of three common types of noise and their applications in Chapter 1, followed by the introduction of the Mott insulator in Chapter 2 and the strange metal in Chapter 3, especially V2O3 and YbRh2Si2 respectively. Then I introduce our noise measurement setup and calibration process in Chapter 4. In Chapter 5, we show our study of percolation and nano second fluctuators in the V2O3 metal insulator transition, through measuring both the low frequency(below 1MHz) and high frequency(10MHz-1GHz) 1/f noise spectrum dependence on bias and temperature. In Chapter 6, we shows our finding of strongly suppressed shot noise intensity in a YbRh2Si2 nanowire compared with a gold nanowire, and this may indicate the lack of well-defined quasiparticles in this strange metal. In Chapter 7, we discussed possible follow-up research based our projects. Supplementary information including probe design and experiments tips are attached in Appendix.
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    Percolation and nanosecond fluctuators in V2O3 films within the metal-insulator transition
    (2020-08-14) Chen, LiYang; Natelson, Douglas
    Vanadium sesquioxide (V2O3) exhibits a first-order metal-insulator transition (MIT) at 160 K between a low temperature, monoclinic, antiferromagnetic Mott insulator and a high temperature, rhombohedral, paramagnetic, metallic phase. In thin films, due to strain, the transition takes place over a finite temperature range of phase coexistence. Resistive noise measured through electronic transport is a probe of percolation and the fluctuating dynamics of the two-phase domain structure. We measure voltage noise spectra at both low frequencies (up to 100 kHz) and radio frequencies (between 10 MHz and 1 GHz). At low current densities the voltage noise intensity is quadratic in bias current, as expected for resistive fluctuations probed nonperturbatively by the current. The low frequency noise generally resembles flicker-type 1/f^α noise, often taking on the form of Lorentzian noise dominated by a small number of fluctuators as the volume fraction of the insulating phase dominates. Radio frequency noise intensity that is quadratic in the bias current allows identification of resistance fluctuations with lifetimes below 1 ns, approaching timescales seen in non-equilibrium pump-probe studies of the transition. Noise at higher current densities show non-quadratic bias dependence, implying current-driven changes to the domain dynamics. We find quantitative consistency with a model for fluctuations in the percolative fraction, though thermodynamic analysis implies that switching of domains between metal and insulator phases can only happen on spatial scales comparable to a unit cell.