Coherent Control of a Metastable Hidden Phase

J. Maklar,1 S. Dong,1 J. Sarkar,1 T. Pincelli,1 P.S. Kirchmann,2 J.A. Sobota,2 S. Yang,2 R.G. Moore,2 Z.-X. Shen,2 S. Beaulieu,1,3 M. Wolf,1 Y.A. Gerasimenko,4,5,6 D. Mihailovic,4,5 R. Ernstofer,1,7 L. Rettig1

1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, Berlin, Germany

2Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA

3Université de Bordeaux – CNRS – CEA, CELIA, UMR5107, F33405, Talence, France

4Dept. of Complex Matter, Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia

5Center of Excellence on Nanoscience and Nanotechnology, Jamova 39, SI-1000 Ljubljana, Slovenia

6Department of Physics, University of Regensburg, Regensburg, Germany

7Institut für Optik und Atomare Physik, Technische Universität Berlin, Straße des 17. Juni 135, Berlin, Germany

Controlling material properties by illumination with ultrashort optical pulses is a promising new pathway to extend the functionality of complex solids. Prominent examples of this rapidly growing research field include photostabilization of superconductivity [1] and switching to metastable states not accessible in thermal equilibrium [2]. A metastable state of particular interest is the optically or electrically induced hidden phase of 1T-TaS2, as it features an order-of-magnitude change in resistivity [3], which allows for novel energy-efficient high-speed memory devices [4]. However, so far a clear understanding of the microscopic processes that govern the dynamic pathways to metastable states is still missing, limiting controllability due to empirical and unspecific switching protocols.

Here, using time- and angle-resolved photoemission spectroscopy (trARPES), we investigate the electronic band structure and ultrafast photoinduced phase transition from commensurate charge-density-wave (CDW) ground state to the hidden state in 1T-TaS2. Mapping the band structure of the hidden state reveals suppression of correlation effects and confirms metallization, suggesting a critical role of interlayer stacking order of the TaS2 sheets in the hidden state. Next, we track the fluence-dependent electron dynamics upon photoexcitation and find strong evidence that the CDW amplitude mode governs a collective, ultrafast switching pathway to the hidden state. This is further corroborated by demonstrating coherent control of the switching efficiency into the hidden phase by controlling the CDW amplitude mode using a multi-pump-pulse excitation scheme. We envision that the amplitude-mode governed transition applies to a range of CDW compounds [5].

1. M. Budden et al., Nat. Phys. 17, 611-618 (2021)
2. V.R. Morrison et al., Science 346, 6208 ( 2014)
3. L. Stojchevska et al., Science 344, 6180 (2014)
4. A. Mraz et al., arXiv preprint 2103.04622 (2021)
5. N. Yoshikawa et al., Nat. Phys. 17, 909-914 (2021)

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