Using angle-resolved photoemission spectroscopy, combined with first principle and coupled self-consistent Poisson-Schrödinger calculations, we demonstrate that potassium (K) atoms adsorbed on the low-temperature phase of 1T-TiSe_{2} induce the creation of a two-dimensional electron gas (2DEG) and quantum confinement of its charge-density wave (CDW) at the surface. By further changing the K coverage, we tune the carrier density within the 2DEG that allows us to nullify, at the surface, the electronic energy gain due to exciton condensation in the CDW phase while preserving a long-range structural order. Our Letter constitutes a prime example of a controlled exciton-related many-body quantum state in reduced dimensionality by alkali-metal dosing.

Département de Physique and Fribourg Center for Nanomaterials Université de Fribourg CH 1700 Fribourg Switzerland

Department of Quantum Matter Physics University of Geneva 24 Quai Ernest Ansermet 1211 Geneva 4 Switzerland

Fritz Haber Institute der Max Planck Gesellschaft Faradayweg 4 6 14195 Berlin Germany

Haute école d'ingénierie et d'architecture de Fribourg CH 1700 Fribourg Switzerland

Institut Jean Lamour UMR 7198 CNRS Université de Lorraine Campus ARTEM 2 allée André Guinier BP 50840 54011 Nancy France

New Technologies Research Centre University of West Bohemia CZ 30100 Pilsen Czech Republic

Univ Rennes CNRS UMR 6251 F 35000 Rennes France

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