16:00-16:40 Peter Liljeroth (Aalto University, Finland)
「Designer quantum states in van der Waals heterostructures」
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Van der Waals (vdW) heterostructures can be used to realize exotic quantum states not found in naturally occurring materials. I will describe our recent results on realizing topological superconductivity [1,2] and artificial heavy fermion systems in vdW heterostructures [3]. We use molecular-beam epitaxy (MBE) and low-temperature scanning tunneling microscopy (STM) for the sample growth and characterization. Topological superconductivity requires combining out of plane ferromagnetism, Rashba-type spin-orbit interactions and s-wave superconductivity, and we use monolayer ferromagnet CrBr3 on a superconducting NbSe2 substrate to realize this [1,2]. In the second part of the talk, I focus on our experiments on 1T-TaS2 / 1H-TaS2 heterostructures that bring together the building blocks of heavy fermion systems – Kondo coupling between a lattice of localized magnetic moments and mobile conduction electrons. These examples highlight the versatility of vdW heterostructures in realizing quantum states that are difficult to find and control in naturally occurring materials.
16:45-17:25 Eli Zeldov (Weizmann Institute of Science, Israel)
「Nanoscale thermal imaging: Glimpse into dissipation in quantum systems down to atomic scale」
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Energy dissipation is a fundamental process governing the dynamics of classical and quantum systems. Despite its vital importance, direct imaging and microscopy of dissipation in quantum systems is currently mostly inaccessible because the existing thermal imaging methods lack the necessary sensitivity and are unsuitable for low temperature operation. We developed a scanning nanoSQUID that resides at the apex of a sharp pipette acting simultaneously as nanomagnetometer with single spin sensitivity and as nanothermometer providing cryogenic thermal imaging with four orders of magnitude improved thermal sensitivity of below 1 µK [1]. The non-contact non-invasive thermometry enables direct visualization and control of the minute heat generated by electrons scattering off a single atomic defect in graphene [2]. By further combining the scanning nanothermometry with simultaneous scanning gate microscopy we demonstrate independent imaging of work and dissipation and reveal the microscopic mechanisms that conceal the true topological protection in the quantum Hall state in graphene [3].
17:30-18:10 Milan P. Allan (Leiden University, Netherlands)
「Electron pairs without superconductivity in a disordered superconductor」
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The idea that preformed electron pairs could exist in a superconductor above its zero-resistance state has been explored for unconventional, interface, and disordered superconductors, yet direct experimental evidence is lacking. In this talk, I will introduce new instrumentation that can unambiguously detect and quantify the number of electron pairs in a sample: the electron pair microscope [1-3]. Applying it to the disordered superconductor titanium nitride, we show that the majority of electrons is paired up to temperatures much higher than the zero-resistance critical temperature Tc, by observing a clear enhancement in the shot noise that is equivalent to a change of the effective charge from 1 to 2 electron charges [4]. We further show that spectroscopic gap fills up rather than closes when increasing temperature. Our results thus demonstrate the existence of a novel state above Tc that, much like an ordinary metal, has no (pseudo)gap, but carries charge entirely via paired electrons.
9:00-9:40 Jiaqi Zhang (Japan Advanced Institute of Science and Technology, Japan)
「atomic scale mechanics studied by in-situ transmission electron microscopy with a quartz length-extension resonator」
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In this study, we developed an in-situ TEM holder equipped with a quartz resonator as force sensor to measure the mechanical properties of atomic scale materials when observing their atomic configurations. A quartz length-extension resonator (LER) was used to measure the stiffness of the materials by the frequency modulation method. The LER has the advantage to reduce its oscillation amplitude below 50 pm, thus we can observe atomic resolved TEM images under the condition of sensor oscillating. The stiffness of platinum (Pt) monatomic chains with 2-5 atoms were measured. The atomic resolution TEM images and videos were captured simultaneously with measuring the conductance and stiffness by our developed TEM holder. We investigated the stiffness of about 150 Pt monatomic chains for reproducibility and confirmed that the middle bond stiffness (25N/m) in the chain was slightly higher than that of the bond connect to the suspending tip (23N/m). In addition, the maximum elastic strain of individual bond in the chain is as large as 24%. These values are obviously different from the bulk counterpart. Such peculiar values can be briefly explained by the concept of “string tension”.
9:45-10:25 Soohyon Phark (Institute for basic science, Korea)
「Atomic Scale Electron Spin Resonance: towards Electron Spin Qubits on a Surface」
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Scanning tunneling microscope (STM) equipped with pulsed electron spin resonance (ESR) enabled coherent spin control of individual atoms [1] and molecules [2] on surfaces. To date magnetic resonance in STM has relied on the modulation of the atomic scale local magnetic interaction between the spin and the STM tip [3,4,5], confining ESR in STM available for only one atom at a time. The poor coherence of the spins in the tunnel junction due to the tunneling electrons [1,2,6] severely restricts an application of the spins in STM to qubit control. Here, we introduce a new way of driving the magnetic resonance of a single atom in STM by the interaction with a single atom magnet in proximity. Pulsed ESR of a single Ti atom on MgO(100) with an Fe atom located in 5-10 Å away showed a non-vanishing Rabi rate ΩRabi, comparable with that driven by the interaction with the tip magnetic moment. We applied this new scheme to remotely drive magnetic resonance of a single atom positioned away from the tip, but weakly coupled with another atomic spin in the tunnel junction, which reads out the spin state of the “remote” spin. The spin-magnet pair provides a feasible building block of on-surface spin qubits, deserving a coherent control of multi qubits on a surface with an enhanced spin coherence.
Toshu An (JAIST)/安東秀(北陸先端大) Yousoo Kim (RIKEN)/金有洙(理研) Tetsuo Hanaguri (RIKEN)/花栗哲郎(理研) Yukio Hasegawa (Univ. Tokyo)/長谷川幸雄(東京大) Masahiro Haze (Univ. Tokyo)/土師将裕(東京大) Yoshinori Okada (OIST)/岡田佳憲(沖縄科技大) Yoshiaki Sugimoto (Univ. Tokyo)/杉本宜昭(東京大) Yasuo Yoshida (Kanazawa Univ.)/吉田靖雄(金沢大)
For further questions, please contact to Masahiro Haze (haze -at- issp.u-tokyo.ac.jp). Please replace -at- to @. お問い合わせは土師(haze -at- issp.u-tokyo.ac.jp)まで。 -at-を@に置き換えてください。
