Intrinsic Insulating Ground State in Transition Metal Dichalcogenide TiSe2

The transition metal dichalcogenide TiSe$_2$ has received significant research attention over the past four decades. Different studies have presented ways to suppress the 200~K charge density wave transition, vary low temperature resistivity by several orders of magnitude, and stabilize magnetism or superconductivity. Here we give the results of a new synthesis technique whereby samples were grown in a high pressure environment with up to 180~bar of argon gas. Above 100~K, properties are nearly unchanged from previous reports, but a hysteretic resistance region that begins around 80~K, accompanied by insulating low temperature behavior, is distinct from anything previously observed. An accompanying decrease in carrier concentration is seen in Hall effect measurements, and photoemission data show a removal of an electron pocket from the Fermi surface in an insulating sample. We conclude that high inert gas pressure synthesis accesses an underlying nonmetallic ground state in a material long speculated to be an excitonic insulator.Comment: 11 pages, 7 figure

Discovery of Superconductivity and Electron-Phonon Drag in the Non-Centrosymmetric Semimetal LaRhGe3_3

We present a comprehensive study of the non-centrosymmetric semimetal LaRhGe$_3$. Our transport measurements reveal evidence for electron-hole compensation at low temperatures, resulting in a large magnetoresistance of 3000% at 1.8 K and 14 T. The carrier concentration is on the order of $10^{21}\rm{/cm}^3$, higher than typical semimetals. We predict theoretically the existence of $\textit{almost movable}$ Weyl nodal lines that are protected by the tetragonal space group. We discover superconductivity for the first time in this compound with a $T_{\text c}$ of 0.39(1) K and $B_{\rm{c}}(0)$ of 2.1(1) mT, with evidence from specific heat and transverse-field muon spin relaxation ($\mu \rm{SR}$). LaRhGe$_3$ is a weakly-coupled type-I superconductor, and we find no evidence for time-reversal symmetry breaking in our zero-field $\mu \rm{SR}$. We study the electrical transport in the normal state and find an unusual $\sim T^{3}$ dependence at low temperature while Seebeck coefficient and thermal conductivity measurements reveal a peak in the same temperature range. We conclude that the transport properties of LaRhGe$_3$ in its normal state are strongly influenced by electron-phonon interactions. Furthermore, we examine the temperature dependent Raman spectra of LaRhGe$_3$ and find that the lifetime of the lowest energy $A_1$ phonon is dominated by phonon-electron scattering instead of anharmonic decay

Women with endometriosis have higher comorbidities: Analysis of domestic data in Taiwan

AbstractEndometriosis, defined by the presence of viable extrauterine endometrial glands and stroma, can grow or bleed cyclically, and possesses characteristics including a destructive, invasive, and metastatic nature. Since endometriosis may result in pelvic inflammation, adhesion, chronic pain, and infertility, and can progress to biologically malignant tumors, it is a long-term major health issue in women of reproductive age. In this review, we analyze the Taiwan domestic research addressing associations between endometriosis and other diseases. Concerning malignant tumors, we identified four studies on the links between endometriosis and ovarian cancer, one on breast cancer, two on endometrial cancer, one on colorectal cancer, and one on other malignancies, as well as one on associations between endometriosis and irritable bowel syndrome, one on links with migraine headache, three on links with pelvic inflammatory diseases, four on links with infertility, four on links with obesity, four on links with chronic liver disease, four on links with rheumatoid arthritis, four on links with chronic renal disease, five on links with diabetes mellitus, and five on links with cardiovascular diseases (hypertension, hyperlipidemia, etc.). The data available to date support that women with endometriosis might be at risk of some chronic illnesses and certain malignancies, although we consider the evidence for some comorbidities to be of low quality, for example, the association between colon cancer and adenomyosis/endometriosis. We still believe that the risk of comorbidity might be higher in women with endometriosis than that we supposed before. More research is needed to determine whether women with endometriosis are really at risk of these comorbidities

Transport Properties of Some Layer Compounds

在過去的十年中，準低維度系統（quasi-low-dimensional systems）在凝態物理內吸引了很多的注意。在這篇論文中，我們針對兩個特定的系統進行討論：拓撲絕緣體（topological insulator）和雙晶格不匹配化合物（misfit compound）。拓撲絕緣體的費米面（Fermi surface）位在一個能隙（band-gap）之中，因此本身是絕緣體。但是在這個能隙中，還有一組連續的表面能態（surface states），其中電子的有效質量為零並且自旋極化。表面能態中電子被限制在樣品表面流動，因此為研究準低維度系統中的傳輸性質提供了一個很好的舞台。由於受到時間反演對稱性（time reversal symmetry）的保護，拓撲絕緣體中的表面能態不會被非磁性雜質和缺陷所破壞。根據理論的預測，表面狀態上有著許多不尋常的傳輸特性，可能在自旋電子學（Spintronics）和量子計算（quantum computing）上有很多的應用。雖然表面狀態可以被角分辨光電子能譜（Angle Resolved Photoemission Spectroscopy, ARPES）所看到，從傳輸量測上要分辨表面能態仍然充滿挑戰。這主要是因為很大一部分的訊號來自於塊材電子能帶（bulk electron band），淹沒了來自於表面能態的訊號。在這篇論文中，我們將分析Bi2Se3在單晶和微電子元件（micro-sized device）中的傳輸訊號，並專注於表面能態的鑑定。我們在大磁場下看到明顯的量子震盪（quantum oscillations），它提供了一種識別費米面形狀的方法。由振盪頻率和磁場角度的關係我們推斷訊號主要來自於一個三維的費米面。這表示，電導率主要來自於塊材的電子能帶。我們在Bi2Se3上的研究經驗，將來可以輕易地應用在其他新的拓撲絕緣體表面能態的鑑定上。 準低維度系統中，另外一個有趣的研究對象的是雙晶格不匹配化合物。在這些晶體中，兩種不同晶格常數的層狀化合物互相堆疊，使得整體晶格結構「不匹配」。由於相鄰原子層之間僅靠著凡得瓦力（van-der-Waals force）鍵結，這些化合物也可以被視為一種準低維度系統。其中一個特別有趣的系統，是由電荷密度波（charge density wave, CDW）材料與另外一種材料（通常是半導體）所構成的雙晶格不匹配化合物。這兩種化合物個別都不具有超導性質（superconductivity）。我們發現，他們所構成的雙晶格不匹配化合物在低溫下卻具有超導電性。此外，相鄰原子層之間的電荷轉移（charge transfer）和應力使得這個系統更加複雜和耐人尋味。一般認為，電荷轉移能抑制電荷密度波的形成，並且誘發超導電性。雙晶格不匹配化合物超導體為這個議題提供了一個研究平台。我們將提供幾個分別屬於1T-TaS2和1T-TiSe2系統中，雙晶格不匹配化合物超導體傳輸性質的數據。我們觀察到電荷轉移與電荷密度波抑制的證據。我們的分析顯示，電荷密度波和超導電性之間有著互相競爭的關係。研究更多類似的樣品將有助於確認這種競爭關係