Speaker: Zhang Yuhu, Institute of Modern Physics, Chinese Academy of Sciences
Time: Wednesday, November 6, 15:30.
SETTING: Beihang University
Venue: Meeting Room 511, Block C, Shahe Main Building, North Campus
The completion and operation of CSR, a heavy ion storage ring in the National scientific apparatus, provides an advanced scientific research platform for the basic and applied research of nuclear physics. In recent years, we have set up an isochronous nuclear mass measuring device on CRS, mainly by researchers from the Institute of Modern Physics of Chinese Academy of Sciences. Through international cooperation, we have conducted a series of experimental measurements on the mass of short-lived nuclei, and obtained new or higher-precision data. Based on this, we have studied the frontier scientific problems in nuclear structure and nuclear astrophysics. This report will introduce the above work and future research plans.
2 Vacancy-driven strange metal physics in transition metal rutile nanostructures
Speaker: Juhn-Jong Lin, National Chiao Tung University, Taiwan.
Time: November 5th (Tuesday) at 10:30.
SETTING: Institute of Physics, Chinese Academy of Sciences
Venue: Room 253, Building M
Metal physics beyond the Landau Fermi liquid paradigm is a central topic in contemporary condensed matter science. Its connection with unconventional s uperconductivity is experimentally well established but the conditions under which these enigmatic metals can form has remained perplexing. The routes proposed towards strange metal formation, which includes the two-channel Kondo effect, generally require rather special conditions or fine tuning. Here we report the observation of robust vacancy-driven orbital two-channel Kondo behavior which occurs without fine-tuning, in paramagnetic IrO2 nanowires possessing the rutile structure. We further demonstrate tunability of this unconventional state to its Fermi-liquid coun terpart within the rutile structure through a complementary analysis of antiferromagnetic RuO2 nanowires. Our findings establish the inherent occurrenc e of non-Fermi liquid physics in a class of topological quantum materials, with implications for fundamental research and potential quantum device applications.
3 Intertwined Orders in the Cuprate Superconductor and the Underlying Organization Principle
Speaker: Weng Zhengyu, Institute of Advanced Studies, Tsinghua University.
Time: 14:00 on Wednesday, November 6.
SETTING: Institute of Physics, Chinese Academy of Sciences
Venue: Room 234, Building M
A sensible phenomenology of the complex phase diagram and rich phenomenon in the high-Tc cuprate calls for a microscopic understanding based on general principles. In this talk, I will identify a set of the most essential organization principles for the doped Mott insulator, which are argued to have captured the fundamental physics of the cuprate superconductor. Then I will exemplify their nature as the exotic long-range en tanglement of many-body quantum mechanics by using the exact numerical tools of exact diagonalization and density matrix renormalization group, which are applied to some special cases of finite size/limited geometry to demonstrate the consequences of the general principle. Next, I will focus on the phase diagram relevant to the experiments in the cuprate, and show that it may be unified by a “parent”ground state ansatz constructed based on the organization principles. Here the superconducting state is o f non-BCS nature with modified London equation and new elementary excitations. In particular, the two-gap structure and dichotomy between the nodal and antinodal regimes in the superconducting state, the origin of Fermi arc in the pseudogap regime, and the strange metal behavior in the high-temperature regime will be discussed as part of the emergent phenomenon.
4 Supersymmetric Landau-Ginzburg Tensor Models
Speakers: Chi-Ming Chang (Zhang Qiming), YMSC, Tsinghua.
Time: 14:00 on Wednesday, November 6.
Setting: Institute of Theoretical Physics, Chinese Academy of Sciences
Venue: ITP South Building 6420
Melonic tensor model is a new type of solvable model, where the melonic Feynman diagrams dominate in the large N limit. The melonic dominance, as well as the solvability and the IR stability of the model, relies on a special type of interaction vertex, which generically would not be preserved under renormalization group flow. I will discuss a class of 2d N=(2,2) melonic tensor models, where the non-renormalization of the superpotential protects the melonic dominance. Another important feature of our models is that they admit a novel type of deformations which gives a large IR conformal manifold. At generic point of the conformal manifold, all the flavor symmetries (including the O(N)^{q-1} symmetry) are broken and all the flat directions in the potential are lifted. I will also discuss how the operator spectrum and the chaos exponent depend on the deformation parameters.
5The Role of Transition Dipole Moment in Photocatalysis and Strong Laser Field Driven Dynamics
Speaker: Lu Ruifeng, Nanjing University of Science and Technology
Time: Wednesday, November 6, 15:10.
Unit: Peking University
Venue: Room 212, Middle Building, Physics Building
The electronic band structure and optical property calculations help us to find new photocatalysts with visible light response in theory. However, the appropriate band gap and band alignment sometimes do not mean better light absorption properties. With the help of detailed transition dipole mome nt analysis, we can clearly reveal the catalytic mechanism of photocatalytic water splitting. In addition, our theoretical simulations show that the amplitude and phase of transition dipole moments play an important role in the attosecond transient absorptio n spectra of atomic systems and the high-order harmonic spectra of crystal systems under ultrafast intense laser irradiation.
6In situ techniques for quantum materials
Reporter: Jinfeng Jia, Shanghai Jiao Tong University
Time: November 07 (Thursday) 15:30.
Unit: Tsinghua University
Venue: Zheng Yutong Lecture Hall, Science Building
Recently, quantum materials are the hottest topic in condensed matter physics. As the samples become smaller and smaller, in situ characterizations become more and more important. By combining molecular beam epitaxy (MBE) with STM, ARPES and other techniques, in situ characterizations can be achieved. With atomic precision control of growth, MBE can provide clean and smooth surfaces for STM and ARPES to study. Meanwhile, STM, ARPES and in situ techniques can also provide enough information for MBE to eliminate much of the trial and error during growth, so that one can fabricate the structures that do not exist in nature or cannot be grown by other techniques. Therefore, this kind of combined system can do some unique work which cannot be done by separate instruments.
In this talk, I will introduce several works done with the combined system to demonstrate the strong power of the combination. With help of STM, artificial cluster crystals, i.e. a periodical array of identical nanoclusters can be grown with precise control. Atomically flat Pb thin films, stanene etc. can be grown with MBE and studied with STM. In Pb films on Si(111), we found quantum well states (QWS) form due to the electronic confinement in the film normal direction and novel properties induced by QWS. We also found high quality topological insulat or films can be grown with MBE. Standing waves and Landau levels were observed with low temperature STM and demonstrated the existing of the topologica l surface states and the prohibition of backward-scattering. Topological insulator/superconductor hetero structures are also fabricated for exploring Majorana fermions.
7 Wideband Silicon Nanophotonics for Classical and Quantum Applications
Speaker: Xiyuan Lu, NIST, University of Maryland College Park.
Time: November 8 (Friday) at 15:30.
Unit: Peking University
Venue: Room 212, Middle Building, Physics Building
Recent advances in nanophotonic technology have led to major progress and new promise in wideband nonlinear optics. In this talk, I will discuss our recent efforts in exploring nonlinear nanophotonics across widely separated spectral bands from visible (~650 nm) to telecom (~1550 nm), for both classical and quantum applications. In the classical regime, efficient spectral translation of light is useful for many integrated photonics applications, including spectroscopy, sensing, and metrology, where coherent visible light needs to be generated efficiently on-chip. I will introduce our recent work1 on how to translate telecom light into the vi sible band by stimulated four-wave mixing, a third-order nonlinear optical process, inside a high quality factor silicon nitride microring. The translation efficiency is comparable to the best current second-order nonlinear result and is a record-high value for nanophotonic spectral translation. In the quantum regime, narrow-linewidth, wide-band quantum entanglement is particularly useful in connecting different species of trapped atoms/ions, defect centers and quantum dots to the telecommunications bands for future quantum communication systems. I will discuss our work2 in generating visib le-telecom photon pairs with record-high brightness and efficiency. Time-energy entanglement is generated and then distributed over a 20 km fiber. I wi ll also introduce our exciting new progress in both applications areas, including visible-telecom optical parametric oscillation3 and wideband quantum frequency combs.
8 strong interaction material structure
Speaker: Guo Fengkun, Institute of Theoretical Physics, Chinese Academy of Sciences
Time: November 8 (Friday) at 18:30.
SETTING: University of Chinese Academy of Sciences
Venue: 1-108, Yanqi Lake Campus.
Strong interaction is one of the basic interactions in nature. Its basic theory is Quantum Chromodynamics (QCD). The non-perturbation interaction of QCD in the low energy region produces hadrons with proton and neutron singlets, which are the source of most mass of visible matter in the universe. Therefore, it is extremely important and challenging to study the material structure of low energy QCD. Since 2003, a large number of new hadron states have been found in high-energy physics experiments around the world, which are completely different from the predictions of the previous successful quark potential model. The study of them has expanded our understanding of hadron structure. In this report, I will introduce the experimental findings and theoretical progress of hadron structure in recent years, including charm meson, ⅹ yz state and pentaquark state.
9Hidden Bridge between Quantum Experiments and Graph Theory
Speaker: Gu Xuemei, Nanjing University.
Time: November 11th (next Monday) at 15:30.
Unit: Peking University
Venue: Room 212, Middle Building, Physics Building
Experiments in laboratories are unquestionably crucial to increase our understanding of quantum systems and inspire new insights into future applicatio ns. However, results of quantum experiments are perfectly computable – but often elude human logic. In this talk, we will present a hidden bridge between quantum experiments and graph theory to show how one can model and understand modern-day photonic quantum exper iments. First we will explain how questions in quantum physics can be translated and answered using Graph theory, while questions in graph theory can be converted and answered in quantum experiments. Then we introduce one important perspective is that complex weigh ts in the graph naturally describe the quantum interference which happens when many photons are involved. This quantum interference is the basis of a n ew special-purpose scheme of quantum computation, which can be exploited to solve Graph Theory questions that are intractable on a classical computer. In the end, our new connection between these seemingly unrelated fields also revealed new insights into quantum state generation with current photonic technology u sing linear optics and probabilistic sources. In general, the bridge gives us a new perspective on photonic quantum technologies and will be significant for the design of future experiments and applications in quantum information.
More report information: list of academic lectures on periodical network of Chinese Physical Society.