Polar metal phase stabilized in strained La-doped BaTiO3films

Ferroelectric polarization and metallic conduction are two seemingly irreconcilable properties that cannot normally coexist in a single system, as the latter tends to screen the former. Polar metals, however, defy this rule and have thus attracted considerable attention as a new class of ferroelectrics exhibiting novel properties. Here, we fabricate a new polar metal film based on the typical ferroelectric material BaTiO₃by combining chemical doping and epitaxial strain induced by a substrate. The temperature dependences of the c-axis lattice constant and the second harmonic generation intensity of La-doped BaTiO₃films indicate the existence of polar transitions. In addition, through La doping, films become metallic at the polar phase, and metallicity enhancement at the polar state occurs in low-La-doped films. This intriguing behaviour is effectively explained by our first-principles calculations. Our demonstration suggests that the carrier doping to ferroelectric material with epitaxial strain serves as a new way to explore polar metals.

Nonlinear Electron-Phonon Coupling in Doped Manganites

We employ time-resolved resonant x-ray diffraction to study the melting of charge order and the associated insulator-to-metal transition in the doped manganite Pr_{0.5}Ca_{0.5}MnO_{3} after resonant excitation of a high-frequency infrared-active lattice mode. We find that the charge order reduces promptly and highly nonlinearly as function of excitation fluence. Density-functional theory calculations suggest that direct anharmonic coupling between the excited lattice mode and the electronic structure drives these dynamics, highlighting a new avenue of nonlinear phonon control.

A magnetic heterostructure of topological insulators as a candidate for an axion insulator

The axion insulator which may exhibit an exotic quantized magnetoelectric effect is one of the most interesting quantum phases predicted for the three-dimensional topological insulator (TI). The axion insulator state is expected to show up in magnetically doped TIs with magnetizations pointing inwards and outwards from the respective surfaces. Towards the realization of the axion insulator, we here engineered a TI heterostructure in which magnetic ions (Cr) are modulation-doped only in the vicinity of the top and bottom surfaces of the TI ((Bi,Sb)₂Te₃) film. A separation layer between the two magnetic layers weakens interlayer coupling between them, enabling the magnetization reversal of individual layers. We demonstrate the realization of the axion insulator by observing a zero Hall plateau (ZHP) (where both the Hall and longitudinal conductivity become zero) in the electric transport properties, excluding the other possible origins for the ZHP. The manifestation of the axion insulator can lead to a new stage of research on novel magnetoelectric responses in topological matter.

Observation of anomalous Hall effect in a non-magnetic two-dimensional electron system

Anomalous Hall effect, a manifestation of Hall effect occurring in systems without time-reversal symmetry, has been mostly observed in ferromagnetically ordered materials. However, its realization in high-mobility two-dimensional electron system remains elusive, as the incorporation of magnetic moments deteriorates the device performance compared to non-doped structure. Here we observe systematic emergence of anomalous Hall effect in various MgZnO/ZnO heterostructures that exhibit quantum Hall effect. At low temperatures, our nominally non-magnetic heterostructures display an anomalous Hall effect response similar to that of a clean ferromagnetic metal, while keeping a large anomalous Hall effect angle θ_AHE≈20°. Such a behaviour is consistent with Giovannini-Kondo model in which the anomalous Hall effect arises from the skew scattering of electrons by localized paramagnetic centres. Our study unveils a new aspect of many-body interactions in two-dimensional electron systems and shows how the anomalous Hall effect can emerge in a non-magnetic system.

Abstract P2-01-17: The combination of preoperative computed tomography lymphography and intraoperative fluorescence imaging navigation for sentinel lymph node biopsy of early breast cancer patients

Background: Sentinel lymph nodes (SLN) biopsy has been established as a standard of care in the treatment of early breast cancer. This technique represents a minimally invasive, highly accurate method of axillary staging and is an alternative to conventional axillary lymph node dissection. The combination of the radioisotope and dye-staining methods is the most accurate way to identify SLN. We had reported feasibility and safety of a new technique of SLN identification using fluorescence imaging of indocyanine green (ICG) injection without any need for training. Recently, SLN identification using computed tomography lymphography (CTLG) has been reported in Japan. This study investigated a usefulness of the combination of CTLG and fluorescence imaging for SLN biopsy of early breast cancer patients.

Patients and method: Between January 2013 and March 2016, 296 breast cancer patients without clinical evidence of lymph node metastasis were treated. On the day before the operation, CTLG was performed using 64-row multidetector CT. We performed an intradermal injection in the periareolar area, using 4 ml of contrast agent with 1 ml of local anesthetic. The contrasted lymph route and SLN were identified in reconstructed three-dimensional imaging. The SLN spot was indicated by CT laser light navigator system. We established typical pattern of the lymphography: stain defect of SLN, stagnation of lymphatic route for preoperative diagnosis of metastatic SLN. During the operation, fluorescence images were obtained using the fluorescence imaging system, Photpdynamic Eye (pde-neo, Hamamatsu Photonics Co., Japan). After 0.5 ml dye mixed indigocarmin and ICG was injected intradermally into the periareolar skin, lymphatic route was observed with fluorescence images. SLN biopsy was performed referring to the point by axillary compression technique by plastic device. Intraoperative pathological analysis of SLN was examined.

Results: The median age of the 296 patients was 59 (range 28 – 90) years old. One patient was male and others were female. CTLG and fluorescence imaging were safely performed in all patients. CTLG could visualize lymphatic route and accurately identify SLN in 284 (95.9 %) and 290 (98.0 %) cases, respectively, whereas fluorescence imaging identified successfully lymphatic route and SLN in all patients. Lymphatic routes of CTLG were completely consistent with those of fluorescence imaging. The number of SLN identified by CTLG was significantly lower than that by fluorescence imaging (1.1 vs. 1.6, p<0.01). Thirty-nine of 296 patients had metastatic SLN pathologically, and 10 of them had micrometastases of SLNs. The accuracy for metastatic diagnosis of SLN using CTLG without micrometastasis was 83.9 %, sensitivity was 82.1 % and specificity was 84.1 %. The positive predictive value was 35.9 % and negative predictive value was 97.7 %.

Conclusion: The combination of CTLG and fluorescence imaging revealed easy and effective to detect SLN. The fluorescence imaging was more high detection rate and number of SLN than CTLG. Otherwise, preoperative diagnosis of SLN metastasis using CTLG would be useful to detect negative SLNs.

Citation Format: Abe H, Teramoto A, Yamasaki K, Yoneda K, Ogawa M, Kawasaki M, Kameyama M. The combination of preoperative computed tomography lymphography and intraoperative fluorescence imaging navigation for sentinel lymph node biopsy of early breast cancer patients [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-01-17.

Large Unidirectional Magnetoresistance in a Magnetic Topological Insulator

We report current-direction dependent or unidirectional magnetoresistance (UMR) in magnetic or nonmagnetic topological insulator (TI) heterostructures, Cr_{x}(Bi_{1-y}Sb_{y})_{2-x}Te_{3}/(Bi_{1-y}Sb_{y})_{2}Te_{3}, that is several orders of magnitude larger than in other reported systems. From the magnetic field and temperature dependence, the UMR is identified to originate from the asymmetric scattering of electrons by magnons. In particular, the large magnitude of UMR is an outcome of spin-momentum locking and a small Fermi wave number at the surface of TI. In fact, the UMR is maximized around the Dirac point with the minimal Fermi wave number.

Evolution of Insulator-Metal Phase Transitions in Epitaxial Tungsten Oxide Films during Electrolyte-Gating

An interface between an oxide and an electrolyte gives rise to various processes as exemplified by electrostatic charge accumulation/depletion and electrochemical reactions such as intercalation/decalation under electric field. Here we directly compare typical device operations of those in electric double layer transistor geometry by adopting A-site vacant perovskite WO3 epitaxial thin films as a channel material and two different electrolytes as gating agent. In situ measurements of X-ray diffraction and channel resistance performed during the gating revealed that in both the cases WO3 thin film reaches a new metallic state through multiple phase transitions, accompanied by the change in out-of-plane lattice constant. Electrons are electrostatically accumulated from the interface side with an ionic liquid, while alkaline metal ions are more uniformly intercalated into the film with a polymer electrolyte. We systematically demonstrate this difference in the electrostatic and electrochemical processes, by comparing doped carrier density, lattice deformation behavior, and time constant of the phase transitions.

Zero-bias photocurrent in ferromagnetic topological insulator

Magnetic interactions in topological insulators cause essential modifications in the originally mass-less surface states. They offer a mass gap at the Dirac point and/or largely deform the energy dispersion, providing a new path towards exotic physics and applications to realize dissipation-less electronics. The nonequilibrium electron dynamics at these modified Dirac states unveil additional functions, such as highly efficient photon to spin-current conversion. Here we demonstrate the generation of large zero-bias photocurrent in magnetic topological insulator thin films on mid-infrared photoexcitation, pointing to the controllable band asymmetry in the momentum space. The photocurrent spectra with a maximal response to the intra-Dirac-band excitations can be a sensitive measure for the correlation between Dirac electrons and magnetic moments.

By magnetic-doping, the electronic band structure of a topological insulator can be significantly altered to yield functional behaviour. Here, the authors demonstrate a large photocurrent response, and its control, under zero-bias in an optimally-designed magnetically-doped topological insulator thin film.