Ultrafast spectroscopy and scanning microscopy of quantum matter
We are about to move into the new physics building in Jiangwan campus…
We use superconducting quantum interference devices and ultrafast laser to study quantum materials, including topological insulators and unconventional superconductors, whose edge, surface, interface characteristics and 2D limit are mainly focused.
Topological insulator is a semiconductor with a protected surface state. The surface state is point spin polarization, which facilitates the powerless transmission of information based on electron spin, which may be used in Spintronics. Theoretically, Majorana fermions may exist when topological insulators and superconductors are combined. This novel particle can play the role of a quantum bit in topological quantum calculation. Thus, finding Majorana fermions will be one of the main directions in our recent exploration. The scanning superconducting quantum interferometer (SQUID) is the most important concept of superconducting integrated circuits．Mastering its design and preparation will make it possible to manufacture the complex superconducting integrated circuits. These technologies with high frequencies (greater than 100 GHz) and low energy consumption will innovate existing transistor-based semiconductor integrated circuits, and they are also a promising way to achieve quantum computing．
Time-and-angle-resolved photoemission spectroscopy (ARPES)
Time-and-angle-resolved photoemission spectroscopy (ARPES), is a direct experimental technique to observe the distribution of the electrons (more precisely, the density of single-particle electronic excitations) in the reciprocal space of solids.It gives information on the direction, speed and scattering process of valence electrons in the sample being studied (usually a solid). This means that information can be gained on both the energy and momentum of an electron, resulting in detailed information on band dispersion and Fermi surface. In our lab, we make use of High Harmonic Generation Laser to be the light source, so that we can do the time-resolved ARPES, using this feature, we can learn the changing of materials’ surface state in a period of time.
Molecular beam epitaxy
Molecular beam epitaxy is a new technique of crystal growth. The method is to place the substrate in an ultra-high vacuum chamber and place the single crystal material to the spray furnace (also in the cavity), depending on the elements. The molecular stream ejected from each element heated to the respective temperature can grow extremely thin (thinner to monatomic layer) single crystals and several alternating superlattice structures on the substrate. Molecular beam epitaxy is mainly studied in different structures or different materials of crystal and superlattice growth. The advantage of this technology is that the growth temperature is low, and it can strictly control the thickness of epitaxial layer components and doping concentration.
There are three elements in the molecular beam epitaxy of our lab, Fe, Te and Bi, respectively. It is mainly used in the growth of FeTe and Bi2Te3. In addition, we installed quartz crystal monitor in the molecular beam epitaxy, which used to measure the beam of elements.
Scanning Superconducting Quantum Interference Device
SQUID is a technique for magnetic measurement, but traditional SQUID apparatus is incapable for testing the magnetism of a thin fim, so we need to seek solution in sSQUID(scanning superconducting quantum interference device), whose sensitivity is 〖10〗^13 higher than traditional SQUID.In asSQUID measurement, we use a nano-SQUID chip to approach the sample and scan through its surface to collect its magnetic signals. The signal is collected by a pick-up loop fabricated on the sSQUID probe, the very close distance between the pick-up loop and the sample strongly enhance the testing sensitivity. The probe also contains a field coil for magnetic susptibility measurement.
The nano scale cryostat provides the working environment for our sSQUID device. A fancy design allow us to switch the sample’s temperature in a large scale when the sSQUID probe is still at its working temperature, thus making it possible to carry out a temperature dominant magnetism measurement. The cryostat also provides SMA connectors and laser windows for ac SQUID experiments and ultra fast laser based SQUID experiments, these parts are still in construction and it is both challenging and exciting to build such a powerful equipment.
Group photo 2017
Nanobridge-based Scanning SQUID Microscopy’s design and fabrication
1. Z. C. Zhang * , Y. H. Wang * , Q. Song, C. Liu, R. Peng, K. A. Moler, D. L. Feng, Y. Wang, “Onset of the Meissner effect at 65K in FeSe thin film grown on Nb-doped SrTiO3 substrate”, Science Bulletin 60 (14), 1301-1304 (2015)
2. M. Xia, J. Jiang, Z. R. Ye, Y. H. Wang, Y. Zhang, S. D. Chen, X. H. Niu, D. F. Xu, F. Chen, X. H. Chen, B. P. Xie, T. Zhang, D. L. Feng, “Angle-resolved Photoemission Spectroscopy Study on the Surface States of the Correlated Topological Insulator YbB6”, Scientific Reports 4, 5999 (2014)
3. Y. H. Wang, H. Steinberg, P. Jarillo-Herrero, N. Gedik, “Observation of Floquet-Bloch states on the surface of a topological insulator”,Science 342, 453 (2013) (featured in MIT news)
4. B. M. Fregoso, Y. H. Wang, N. Gedik, and V. Galitski, “Driven electronic states at the surface of a topological insulator”, Phys. Rev. B 88, 155129 (2013)
5. Yihua Wang, and Nuh Gedik, “Circular dichroism in angle-resolved photoemission spectroscopy of topological insulators”, Phys. Status Solidi RRL 7, 64 (2013) (invited review)
6. Y. H. Wang, D. Hsieh, E. J. Sie, H. Steinberg, D. R. Gardner, Y. S. Lee, P. Jarillo-Herrero, and N. Gedik, “Measurement of intrinsic Dirac fermion cooling on the surface of a topological insulator Bi2Se3 using time- and angle-resolved photoemission spectroscopy”, Phys. Rev. Lett. 109, 127401 (2012) (featured in Physics Synopsis, MIT news and NBC news)
7. Y. H. Wang, and N. Gedik, “Electron pulse compression with a practical reflectron design for ultrafast electron diffraction”, IEEE Journal of Selected Topics in Quantum Electronics 18, 140 (2012)
8. Y. H. Wang, D. Hsieh, D. Pilon, L. Fu, D. R. Gardner, Y. S. Lee and N. Gedik, “Observation of a warped helical spin texture in Bi2Se3 from circular dichroism angle-resolved photoemission spectroscopy”, Phys. Rev. Lett. 107, 207602 (2011) (featured in MIT news)
9. S. E. Maxwell, M. T. Hummon, Y. H. Wang, A. A. Buchachenko, R. V. Krems, and J. M. Doyle, “Spin-orbit interaction and large inelastic rates in bismuth-helium collisions”, Phys. Rev. A 78, 042706 (2008)
10. M.T. Hummon, W.C. Campbell, H. Lu, E. Tsikata, Y. H. Wang, and J.M. Doyle, “Magnetic trapping of atomic nitrogen and cotrapping of NH”, Phys. Rev. A 78, 050702(R) (2008)
11. K. Yang, B. P. Xie, D. W. Shen, J. F. Zhao, H. W. Ou, J. Wei, S. Wang, Y. H. Wang, D.H. Lu, R. H. He, M. Arita, A. Ino, H. Namatame, M. Taniguchi, F. Q. Xu, H. Eisaki, N. Kaneko, D. L. Feng, “Electronic structure in the heavily overdoped regime of Bi2Sr2CuO6+d cuprate superconductors”, Phys. Rev. B 73, 144507 (2006)
If you are interested in the exciting field of quantum matter, please contact Prof. Wang: firstname.lastname@example.org
Undergraduates and postgraduates are all welcomed!
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Prof. YiHua Wang
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