AQP Seminar: Charge density and spin waves low frequency noise

Aalto Quantum Physics Seminar (Nanotalo). Speaker: Prof. Sergey Rumyantsev (Institute of High Pressure Physics Warsaw, University of California)

The charge-density-wave (CDW) phase is a macroscopic quantum state consisting of a periodic modulation of the electronic charge density accompanied by a periodic distortion of the atomic lattice in metallic crystals. The recently renewed interest to these materials has been driven by layer-controlled CDW materials, such as quasi-two-dimensional (2D) crystals of 1T-TaS₂ and other transition metal dichalcogenides (TMDs). Unlike classical bulk CDW materials with the quasi-1D crystalline structure, TMD family exhibit unusually high transition temperatures to various CDW phases. The 2D crystal structure of TMDs allows one to exfoliate or grow layers with few-nanometer thicknesses, creating conditions for greater control of the CDW phase transitions with temperature or electric field, as well as enabling integration with other 2D materials.

One of the most interesting quasi-2D CDW TMD materials is 1T-TaS₂ which undergoes several phase transition at temperatures from 80K to 550K. The 1T-TaS₂ CDW devices, operational at room temperature (RT), exhibit high radiation hardness, and can be used for high frequency and information processing applications.

Another field of study which is rapidly developing now and also deals with waves, but waves of spins (not charges) is magnonics. Magnon current, i.e. spin waves, can be used for information processing, sensing, and other applications. A possibility of using the amplitude and phase of magnons for sending signals via electrical insulators creates conditions for avoiding Ohmic losses, and achieving ultra-low power dissipation. The sensitivity and selectivity of magnonic sensors is limited by the low frequency noise. However, the fundamental question “do magnons make noise?” has not been answered yet.

We have demonstrated that low frequency noise spectroscopy is effective for studying the electron transport, depinning and sliding of CDW, identifying the CDW potential “hidden states”, and study the magnon currents.